Re: Difference between a force and a velocity ?
Please, just let me have a little bit of peril! Sent from my iPhone On Feb 14, 2013, at 6:53 PM, Eric Lampi ericla...@gmail.com wrote: Albatross! On Thu, Feb 14, 2013 at 7:32 PM, Ed Manning etmth...@gmail.com wrote: NI! NI! NI! NINININ On Thu, Feb 14, 2013 at 7:17 PM, Simon Anderson simonbenandersonl...@gmail.com wrote: Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.com wrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.com wrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/ -- Freelance 3D and VFX animator http://vimeopro.com/user7979713/3d-work
Re: Difference between a force and a velocity ?
Interesting thread - I never really thought about the technical aspects of that. On 2/13/2013 12:37 PM, Leonard Koch wrote: Apologies, there are a couple of number typos in the first one. Here is the corrected version: Velocity is the speed and direction at which an object moves. Force is something with a strength and a direction that causes acceleration on the object and has an effect on its velocity. Think about it like this: You have some object, that is flying through space with a VELOCITY. Maybe it is flying upwards, so the DIRECTION it is flying in would be [0, 1, 0]. And let's say that it is flying with a SPEED of 6 units per second. Those are the two components our velocity is made of: In what direction is it flying and how fast is it flying there? In ICE these two values are one vector [0, 6, 0] which you get by multiplying the SPEED (6) with the DIRECTION ([0, 1, 0]). When you multiply a vector(a row of numbers) with a scalar(a single number) you simply multiply each element of the vector with the scalar. [6*0, 6*1, 6*0] = [0, 6, 0] = the VELOCITY of the object Now there is also the FORCE and this could be for example gravity or a wind blowing, just anything that will move the object. What properties does a force have? It pushes things in a certain DIRECTION. It pushes things with a certain STRENGTH. Let's say our force pushes to the left, so in Softimage it's DIRECTION would be [1, 0, 0]. And let's say that the STRENGTH of the forces push is 8. Once again these two properties of the force are represented in one vector [8, 0, 0] which you get by multiplying the STRENGTH(8) with the DIRECTION ([1, 0, 0]). [8*1, 8*0, 8*0] = [8, 0, 0] = the FORCE. So now that we have a good idea of what a force and a velocity are let's see what happens when the force acts upon our little object. The object is moving through space with the VELOCITY [0, 6, 0] and suddenly there is the FORCE [8, 0, 0] acting on it. Maybe an interstellar wind started blowing... The FORCE is acting on the object and wants to push it in another direction/speed, which would give it a new VELOCITY since velocity = speed*direction. But the object also has MASS, that is a measure of how resistant to changing velocity an object is. Let's say it has the MASS 4. Now the force is still going to change the velocity of the object, but the effect will be reduced by the mass. The formula for how it is going to be reduced by the mass, comes from the famous formula F=m*a ( force = mass * acceleration ) If we divide both sides of that equation by mass we get: F/m = a ( force / mass = acceleration) This tells us that we must divide our FORCE (F) by the MASS (m) to get the acceleration. Force: [8, 0, 0] Mass: 4 [8, 0, 0] / 4 = [8/4, 0/4, 0/4 = [2, 0, 0] = acceleration Now all you have to do once you have computed your acceleration is to add it your velocity, to see what new velocity the force pushed it in. So: PreForceVelocity + acceleration = PostForceVelocity Velocity = [0, 6, 0] Acceleration = [2, 0, 0] [0, 6, 0] + [2, 0, 0] = [0+2, 6+0, 0+0] = [2, 6, 0] = PostForceVelocity After our Object travelling with a mass of 4 and a velocity of [0, 6, 0] interacted with a force of [8, 0, 0] its new velocity is [2, 6, 0] A bit elaborate, but I hope it helps you gain some intuition. On Wed, Feb 13, 2013 at 12:24 PM, Leonard Koch leonardkoch...@gmail.com mailto:leonardkoch...@gmail.com wrote: Velocity is the speed and direction at which an object moves. Force is something with a strength and a direction that causes acceleration on the object and has an effect on its velocity. Think about it like this: You have some object, that is flying through space with a VELOCITY. Maybe it is flying upwards, so the DIRECTION it is flying in would be [0, 1, 0]. And let's say that it is flying with a SPEED of 6 units per second. Those are the two components our velocity is made of: In what direction is it flying and how fast is it flying there? In ICE these two values are one vector [0, 6, 0] which you get by multiplying the SPEED (5) with the DIRECTION ([0, 1, 0]). When you multiply a vector(a row of numbers) with a scalar(a single number) you simply multiply each element of the vector with the scalar. [6*0, 6*1, 6*0] = [0, 6, 0] = the VELOCITY of the object Now there is also the FORCE and this could be for example gravity or a wind blowing, just anything that will move the object. What properties does a force have? It pushes things in a certain DIRECTION. It pushes things with a certain STRENGTH. Let's say our force pushes to the left, so in Softimage it's DIRECTION would be [1, 0, 0]. And let's say that the STRENGTH of the forces push is 8. Once again these two properties of the force are represented in one vector [2, 0, 0] which you get by multiplying the STRENGTH(8) with the DIRECTION ([1, 0, 0]).
RE: Difference between a force and a velocity ?
Like I said multiple times already. Take it up with the physicists and mathematicians. The example given is from a physics text book. You got a problem, take it up with the author. Sheesh! From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Alok Gandhi Sent: Thursday, February 14, 2013 5:15 AM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? If you have a problem with that, take it up with the physicists and mathematicians. Sorry Matt but I think you're wrong, and you can consider me a mathematician (I have a Masters in Mathematics and a Bachelor in Physics, Chemistry and Mathematics). Just taking a pure math approach now to set things right. Velocity is a vector as we know with a magnitude as Speed and a direction. So we can write: [cid:image001.gif@01CE0A9F.DCEA1810] Where 's' is speed and 'v' is velocity and [cid:image002.gif@01CE0A9F.DCEA1810] is the magnitude of the velocity. Now in the above equation, we cannot have 's' as non-zero and 'v' as zero. Because if 's' is zero , 'v' will be zero and if 's' is non-zero so will be 'v'. Here is a reference: http://bit.ly/XOAM50 Cheers ! Alok Gandhi Lead TD Modusfx inline: image001.gifinline: image002.gif
RE: Difference between a force and a velocity ?
The formula [Inline image 1] is valid for instaneous velocity and speed, but not average velocity and speed over an interval. I think that maybe that was the point of the example in the textbook. Suppose we take 4 samples around the track. The average velocity is given by: Vavg = AVG([ 6.66, 0], [0, 6.66], [-6.66, 0], [0, -6.66]) = ([ 6.66, 0] + [0, 6.66] + [-6.66, 0] + [0, -6.66])/4 = [0, 0]/4 = [0, 0] However because speed has no direction (you cannot travel at -10km/h for example), the average speed is given by: Savg = AVG (6.66, 6.66, 6.66, 6.66) = 6.66 Of course, this distinction is secondary to the more important distinction that velocity is a vector (length and direction) while speed is a scalar (magnitude only). gray From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Matt Lind Sent: Thursday, February 14, 2013 01:42 PM To: softimage@listproc.autodesk.com Subject: RE: Difference between a force and a velocity ? Like I said multiple times already. Take it up with the physicists and mathematicians. The example given is from a physics text book. You got a problem, take it up with the author. Sheesh! From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Alok Gandhi Sent: Thursday, February 14, 2013 5:15 AM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? If you have a problem with that, take it up with the physicists and mathematicians. Sorry Matt but I think you're wrong, and you can consider me a mathematician (I have a Masters in Mathematics and a Bachelor in Physics, Chemistry and Mathematics). Just taking a pure math approach now to set things right. Velocity is a vector as we know with a magnitude as Speed and a direction. So we can write: [Inline image 1] Where 's' is speed and 'v' is velocity and [Inline image 2] is the magnitude of the velocity. Now in the above equation, we cannot have 's' as non-zero and 'v' as zero. Because if 's' is zero , 'v' will be zero and if 's' is non-zero so will be 'v'. Here is a reference: http://bit.ly/XOAM50 Cheers ! Alok Gandhi Lead TD Modusfx attachment: winmail.dat
Re: Difference between a force and a velocity ?
In the past 2 years, I attended college courses in Physics 101 and 201 at UT Dallas, as well as a Princeton Review course for the MCAT's which include heavy study in basic physics, especially about the definitions of fundamental units and concepts. As it turns out, Matt is correct in that the example of displacement returning to origin will result in an average velocity of 0. Both my physics professor as well as the Princeton Review instructor took special care to mention this specific example more than once because it is a common trick question on the MCATs. HOWEVER, and this is important. It is absolutely NOT the first and only example provided to explain the difference between velocity and speed. Nor did it come up during the first lecture about velocity. It was brought up long after we had repeatedly reviewed the concept, in an attempt to trip us up in order to demonstrate the exception. Defining velocity and then using zero displacement to explain it is similar to introducing the letter 'p' and using the word 'pneumonia' as your very first example. If you have a problem with that, take it up with the lexicographers and wordsmiths? -B
Re: Difference between a force and a velocity ?
This is one of the most intelligently absurd threads I've ever followed. :)
RE: Difference between a force and a velocity ?
You waterski while twirling a web strand behind you? Pictures or it never happened! gray From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Raffaele Fragapane Sent: Thursday, February 14, 2013 04:58 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? It's fascinating the way a car crash between two vehicles driven by physicists arguing with each other as they are flung out of their seats and through their windscreens would be. Can't take my eyes away, horror and awe together. Ultimately, I'm with Spiderman on this. On Fri, Feb 15, 2013 at 8:49 AM, Andy Moorer andymoo...@gmail.commailto:andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) attachment: winmail.dat
Re: Difference between a force and a velocity ?
If a parrot's velocity is [0,0,0], is it *dead*? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :)
Re: Difference between a force and a velocity ?
Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.comwrote: If a parrot's velocity is [0,0,0], is it *dead*? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.comwrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.com wrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.com wrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.comwrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/
Re: Difference between a force and a velocity ?
NI! NI! NI! NINININ On Thu, Feb 14, 2013 at 7:17 PM, Simon Anderson simonbenandersonl...@gmail.com wrote: Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.comwrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.comwrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/
Re: Difference between a force and a velocity ?
Oh, what sad times are these when passing ruffians can say Ni at will to old ladies. On Thu, Feb 14, 2013 at 7:32 PM, Ed Manning etmth...@gmail.com wrote: NI! NI! NI! NINININ On Thu, Feb 14, 2013 at 7:17 PM, Simon Anderson simonbenandersonl...@gmail.com wrote: Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.comwrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.comwrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/
Re: Difference between a force and a velocity ?
Albatross! On Thu, Feb 14, 2013 at 7:32 PM, Ed Manning etmth...@gmail.com wrote: NI! NI! NI! NINININ On Thu, Feb 14, 2013 at 7:17 PM, Simon Anderson simonbenandersonl...@gmail.com wrote: Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.comwrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.comwrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/ -- Freelance 3D and VFX animator http://vimeopro.com/user7979713/3d-work
Re: Difference between a force and a velocity ?
https://i.chzbgr.com/maxW500/7055969792/h07769A83/ On Thu, Feb 14, 2013 at 4:53 PM, Eric Lampi ericla...@gmail.com wrote: Albatross! On Thu, Feb 14, 2013 at 7:32 PM, Ed Manning etmth...@gmail.com wrote: NI! NI! NI! NINININ On Thu, Feb 14, 2013 at 7:17 PM, Simon Anderson simonbenandersonl...@gmail.com wrote: Bring me a shrubbery On Fri, Feb 15, 2013 at 10:32 AM, Andy Moorer andymoo...@gmail.comwrote: African or European? Hey, Alan started the Monty python references, that made the question mandatory. On Feb 14, 2013, at 6:24 PM, Ed Manning etmth...@gmail.com wrote: laden or un-laden? On Thu, Feb 14, 2013 at 5:55 PM, Ahmidou Lyazidi ahmidou@gmail.com wrote: Schrödinger parrots ? Ahmidou Lyazidi Director | TD | CG artist http://vimeo.com/ahmidou/videos 2013/2/15 Eric Thivierge ethivie...@gmail.com: Is the parrot sitting on a leopard? Eric Thivierge http://www.ethivierge.com On Thu, Feb 14, 2013 at 5:25 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Is it in a forest? And is anybody watching? On Fri, Feb 15, 2013 at 9:22 AM, Alan Fregtman alan.fregt...@gmail.com wrote: If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :) -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are! -- --- Simon Ben Anderson blog: http://vinyldevelopment.wordpress.com/ -- Freelance 3D and VFX animator http://vimeopro.com/user7979713/3d-work
RE: Difference between a force and a velocity ?
Thanks for the validation, Brad. Each instructor has their own methods because this was indeed the first example presented to me when I took physics years ago to make the distinction between speed and velocity. The professor said straight up it would be the very first question on the exam (it was) and anybody who got the question wrong would fail the exam. Nobody failed, to my knowledge. It wasn't treated as a trick question, it was fundamental material. He often reused examples across different topics so we could focus on the relevant new information and cut down the noise/relearning. For example, the running track was reused (with slight modifications) as an introduction to 'work' illustrating no work is performed if there is no displacement. Since he already proved the theory with velocity, he didn't have to waste time re-explaining it for work. While tough at first due to the abstract nature, I found his approach very refreshing as it allowed me to tackle tougher problems because I was exposed to the edge cases upfront and conditioned to not think of them as edge cases. Edge cases are a product of our tools (math) to explain observed behavior. The universe doesn't have a concept of edge case. I think my professor chose this approach because he once mentioned students had problems progressing from newton's laws to quantum mechanics because as they entered more advanced levels, they tended to forget previously learned material still applied (or they didn't see the connection). He conditioned students to think more about the problem rather than merely choose a formula and plug in numbers. Often his toughest problems required the least amount of math to solve. Some of his lectures could be really dry, as he was a dry guy himself, but he was probably the best physics professor I had of many. Matt From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Bradley Gabe Sent: Thursday, February 14, 2013 1:21 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? In the past 2 years, I attended college courses in Physics 101 and 201 at UT Dallas, as well as a Princeton Review course for the MCAT's which include heavy study in basic physics, especially about the definitions of fundamental units and concepts. As it turns out, Matt is correct in that the example of displacement returning to origin will result in an average velocity of 0. Both my physics professor as well as the Princeton Review instructor took special care to mention this specific example more than once because it is a common trick question on the MCATs. HOWEVER, and this is important. It is absolutely NOT the first and only example provided to explain the difference between velocity and speed. Nor did it come up during the first lecture about velocity. It was brought up long after we had repeatedly reviewed the concept, in an attempt to trip us up in order to demonstrate the exception. Defining velocity and then using zero displacement to explain it is similar to introducing the letter 'p' and using the word 'pneumonia' as your very first example. If you have a problem with that, take it up with the lexicographers and wordsmiths? -B
RE: Difference between a force and a velocity ?
Ah - this is where you can tell the difference between a force and a velocity - as if you took your parrot with a volocity of [0,0,0] and gave it a force of your foot in it's butt [Len100] then not only would you find out if the velocity of [0,0,0] meant it was dead, but you would also change the velocity to [100,0,0] S. Sandy Sutherlandmailto:sandy.sutherl...@triggerfish.co.za | Technical Supervisor [http://triggerfish.co.za/en/wp-content/uploads/udf_foundry/images/logo.png] http://triggerfish.co.za/en [http://static.ak.fbcdn.net/rsrc.php/v2/ym/x/lFV-lsMcC_0.png] http://www.facebook.com/triggerfishanimation [https://si0.twimg.com/a/1349296073/images/resources/twitter-bird-white-on-blue.png] http://www.twitter.com/triggerfishza From: softimage-boun...@listproc.autodesk.com [softimage-boun...@listproc.autodesk.com] on behalf of Alan Fregtman [alan.fregt...@gmail.com] Sent: 15 February 2013 00:22 To: XSI Mailing List Subject: Re: Difference between a force and a velocity ? If a parrot's velocity is [0,0,0], is it dead? :p On Thu, Feb 14, 2013 at 4:49 PM, Andy Moorer andymoo...@gmail.commailto:andymoo...@gmail.com wrote: This is one of the most intelligently absurd threads I've ever followed. :)
Re: Difference between a force and a velocity ?
They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
Actually speed = distance-traveled/time, velocity is more like position / time (it's a vector). On Wed, Feb 13, 2013 at 11:13 AM, César Sáez cesa...@gmail.com wrote: They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
Try to answer the question, Force will be considering mass as F = m.a, where m is mass, and a is acceleration. While velocity doesn't consider mass. Cheers, On Wed, Feb 13, 2013 at 4:49 PM, olivier jeannel olivier.jean...@noos.frwrote: Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained... -- Daniel Harjanto Infinite Frameworks Studios TD http://misterdi.cgpot.com
Re: Difference between a force and a velocity ?
Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
It's actually incorrect more so than clear. Distance traveled divided by time is not velocity. It's speed, a scalar value. Velocity has to do with the rate of change and is represented by a vector providing direction, and it's magnitude representing speed. So while speed is the simple speed an object travels at, velocity also specifies direction. A force is represented similarly to velocity and has/affects (depending on the approach, generally correct if considered affecting) mass, it's effect results in the affected body's velocity. A force is basically something affecting another entity into change. It can be summarized in push or pull efforts. Acceleration is the rate of change of speed. This is for Newtonian physics, or vectorial physics, the most common kind in CG related models. On Feb 13, 2013 9:52 PM, olivier jeannel olivier.jean...@noos.fr wrote: Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
Reading that after sending it (when else would one proof read?) I realize it might come across as a bit aggressive with the opening comment. My apologies to César if that's the case, it sure wasn't intended to be or to discourage someone else away from contributing to the already rare physics discussions. Oliver, Wikipedia has excellent resources about these subjects, just look up Newtonian physics and wiki hop around to the specific words you wanted the meaning of. On Feb 13, 2013 10:08 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: It's actually incorrect more so than clear. Distance traveled divided by time is not velocity. It's speed, a scalar value. Velocity has to do with the rate of change and is represented by a vector providing direction, and it's magnitude representing speed. So while speed is the simple speed an object travels at, velocity also specifies direction. A force is represented similarly to velocity and has/affects (depending on the approach, generally correct if considered affecting) mass, it's effect results in the affected body's velocity. A force is basically something affecting another entity into change. It can be summarized in push or pull efforts. Acceleration is the rate of change of speed. This is for Newtonian physics, or vectorial physics, the most common kind in CG related models. On Feb 13, 2013 9:52 PM, olivier jeannel olivier.jean...@noos.fr wrote: Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
Velocity is the speed and direction at which an object moves. Force is something with a strength and a direction that causes acceleration on the object and has an effect on its velocity. Think about it like this: You have some object, that is flying through space with a VELOCITY. Maybe it is flying upwards, so the DIRECTION it is flying in would be [0, 1, 0]. And let's say that it is flying with a SPEED of 6 units per second. Those are the two components our velocity is made of: In what direction is it flying and how fast is it flying there? In ICE these two values are one vector [0, 6, 0] which you get by multiplying the SPEED (5) with the DIRECTION ([0, 1, 0]). When you multiply a vector(a row of numbers) with a scalar(a single number) you simply multiply each element of the vector with the scalar. [6*0, 6*1, 6*0] = [0, 6, 0] = the VELOCITY of the object Now there is also the FORCE and this could be for example gravity or a wind blowing, just anything that will move the object. What properties does a force have? It pushes things in a certain DIRECTION. It pushes things with a certain STRENGTH. Let's say our force pushes to the left, so in Softimage it's DIRECTION would be [1, 0, 0]. And let's say that the STRENGTH of the forces push is 8. Once again these two properties of the force are represented in one vector [2, 0, 0] which you get by multiplying the STRENGTH(8) with the DIRECTION ([1, 0, 0]). [8*1, 8*0, 8*0] = [8, 0, 0] = the FORCE. So now that we have a good idea of what a force and a velocity are let's see what happens when the force acts upon our little object. The object is moving through space with the VELOCITY [0, 6, 0] and suddenly there is the FORCE [8, 0, 0] acting on it. Maybe an interstellar wind started blowing... The FORCE is acting on the object and wants to push it in another direction/speed, which would give it a new VELOCITY since velocity = speed*direction. But the object also has MASS, that is a measure of how resistant to changing velocity an object is. Let's say it has the MASS 4. Now the force is still going to change the velocity of the object, but the effect will be reduced by the mass. The formula for how it is going to be reduced by the mass, comes from the famous formula F=m*a ( force = mass * acceleration ) If we divide both sides of that equation by mass we get: F/m = a ( force / mass = acceleration) This tells us that we must divide our FORCE (F) by the MASS (m) to get the acceleration. Force: [8, 0, 0] Mass: 4 [8, 0, 0] / 4 = [8/4, 0/4, 0/4 = [2, 0, 0] = acceleration Now all you have to do once you have computed your acceleration is to add it your velocity, to see what new velocity the force pushed it in. So: PreForceVelocity + acceleration = PostForceVelocity Velocity = [0, 6, 0] Acceleration = [2, 0, 0] [0, 6, 0] + [2, 0, 0] = [0+2, 6+0, 0+0] = [2, 6, 0] = PostForceVelocity After our Object travelling with a mass of 4 and a velocity of [0, 6, 0] interacted with a force of [8, 0, 0] its new velocity is [2, 6, 0] A bit elaborate, but I hope it helps you gain some intuition. On Wed, Feb 13, 2013 at 12:16 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: Reading that after sending it (when else would one proof read?) I realize it might come across as a bit aggressive with the opening comment. My apologies to César if that's the case, it sure wasn't intended to be or to discourage someone else away from contributing to the already rare physics discussions. Oliver, Wikipedia has excellent resources about these subjects, just look up Newtonian physics and wiki hop around to the specific words you wanted the meaning of. On Feb 13, 2013 10:08 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: It's actually incorrect more so than clear. Distance traveled divided by time is not velocity. It's speed, a scalar value. Velocity has to do with the rate of change and is represented by a vector providing direction, and it's magnitude representing speed. So while speed is the simple speed an object travels at, velocity also specifies direction. A force is represented similarly to velocity and has/affects (depending on the approach, generally correct if considered affecting) mass, it's effect results in the affected body's velocity. A force is basically something affecting another entity into change. It can be summarized in push or pull efforts. Acceleration is the rate of change of speed. This is for Newtonian physics, or vectorial physics, the most common kind in CG related models. On Feb 13, 2013 9:52 PM, olivier jeannel olivier.jean...@noos.fr wrote: Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time
Re: Difference between a force and a velocity ?
Apologies, there are a couple of number typos in the first one. Here is the corrected version: Velocity is the speed and direction at which an object moves. Force is something with a strength and a direction that causes acceleration on the object and has an effect on its velocity. Think about it like this: You have some object, that is flying through space with a VELOCITY. Maybe it is flying upwards, so the DIRECTION it is flying in would be [0, 1, 0]. And let's say that it is flying with a SPEED of 6 units per second. Those are the two components our velocity is made of: In what direction is it flying and how fast is it flying there? In ICE these two values are one vector [0, 6, 0] which you get by multiplying the SPEED (6) with the DIRECTION ([0, 1, 0]). When you multiply a vector(a row of numbers) with a scalar(a single number) you simply multiply each element of the vector with the scalar. [6*0, 6*1, 6*0] = [0, 6, 0] = the VELOCITY of the object Now there is also the FORCE and this could be for example gravity or a wind blowing, just anything that will move the object. What properties does a force have? It pushes things in a certain DIRECTION. It pushes things with a certain STRENGTH. Let's say our force pushes to the left, so in Softimage it's DIRECTION would be [1, 0, 0]. And let's say that the STRENGTH of the forces push is 8. Once again these two properties of the force are represented in one vector [8, 0, 0] which you get by multiplying the STRENGTH(8) with the DIRECTION ([1, 0, 0]). [8*1, 8*0, 8*0] = [8, 0, 0] = the FORCE. So now that we have a good idea of what a force and a velocity are let's see what happens when the force acts upon our little object. The object is moving through space with the VELOCITY [0, 6, 0] and suddenly there is the FORCE [8, 0, 0] acting on it. Maybe an interstellar wind started blowing... The FORCE is acting on the object and wants to push it in another direction/speed, which would give it a new VELOCITY since velocity = speed*direction. But the object also has MASS, that is a measure of how resistant to changing velocity an object is. Let's say it has the MASS 4. Now the force is still going to change the velocity of the object, but the effect will be reduced by the mass. The formula for how it is going to be reduced by the mass, comes from the famous formula F=m*a ( force = mass * acceleration ) If we divide both sides of that equation by mass we get: F/m = a ( force / mass = acceleration) This tells us that we must divide our FORCE (F) by the MASS (m) to get the acceleration. Force: [8, 0, 0] Mass: 4 [8, 0, 0] / 4 = [8/4, 0/4, 0/4 = [2, 0, 0] = acceleration Now all you have to do once you have computed your acceleration is to add it your velocity, to see what new velocity the force pushed it in. So: PreForceVelocity + acceleration = PostForceVelocity Velocity = [0, 6, 0] Acceleration = [2, 0, 0] [0, 6, 0] + [2, 0, 0] = [0+2, 6+0, 0+0] = [2, 6, 0] = PostForceVelocity After our Object travelling with a mass of 4 and a velocity of [0, 6, 0] interacted with a force of [8, 0, 0] its new velocity is [2, 6, 0] A bit elaborate, but I hope it helps you gain some intuition. On Wed, Feb 13, 2013 at 12:24 PM, Leonard Koch leonardkoch...@gmail.comwrote: Velocity is the speed and direction at which an object moves. Force is something with a strength and a direction that causes acceleration on the object and has an effect on its velocity. Think about it like this: You have some object, that is flying through space with a VELOCITY. Maybe it is flying upwards, so the DIRECTION it is flying in would be [0, 1, 0]. And let's say that it is flying with a SPEED of 6 units per second. Those are the two components our velocity is made of: In what direction is it flying and how fast is it flying there? In ICE these two values are one vector [0, 6, 0] which you get by multiplying the SPEED (5) with the DIRECTION ([0, 1, 0]). When you multiply a vector(a row of numbers) with a scalar(a single number) you simply multiply each element of the vector with the scalar. [6*0, 6*1, 6*0] = [0, 6, 0] = the VELOCITY of the object Now there is also the FORCE and this could be for example gravity or a wind blowing, just anything that will move the object. What properties does a force have? It pushes things in a certain DIRECTION. It pushes things with a certain STRENGTH. Let's say our force pushes to the left, so in Softimage it's DIRECTION would be [1, 0, 0]. And let's say that the STRENGTH of the forces push is 8. Once again these two properties of the force are represented in one vector [2, 0, 0] which you get by multiplying the STRENGTH(8) with the DIRECTION ([1, 0, 0]). [8*1, 8*0, 8*0] = [8, 0, 0] = the FORCE. So now that we have a good idea of what a force and a velocity are let's see what happens when the force acts upon our little object. The object is moving through space with the VELOCITY [0, 6, 0] and suddenly there is the FORCE
RE: Difference between a force and a velocity ?
Velocity = net displacement / time. Force = Mass * Acceleration NOTE: Speed and velocity are very different. Speed is distance traveled over time (scalar) Velocity is net displacement over time (vector) Example: Running around a track in a stadium. If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position. Matt -Original Message- From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of olivier jeannel Sent: Wednesday, February 13, 2013 1:50 AM To: softimage@listproc.autodesk.com Subject: Difference between a force and a velocity ? Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained...
Re: Difference between a force and a velocity ?
is that distinctions helpful here? i mean we aren't just going to render the last frame of our particle going around the track, we are going to render 1440 frames (24fps*60secs) and at each frame the instantaneous velocity is going to have some direction and magnitude. On Wed, Feb 13, 2013 at 11:13 AM, Matt Lind ml...@carbinestudios.comwrote: Velocity = net displacement / time. Force = Mass * Acceleration NOTE: Speed and velocity are very different. Speed is distance traveled over time (scalar) Velocity is net displacement over time (vector) Example: Running around a track in a stadium. If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position. Matt -Original Message- From: softimage-boun...@listproc.autodesk.com [mailto: softimage-boun...@listproc.autodesk.com] On Behalf Of olivier jeannel Sent: Wednesday, February 13, 2013 1:50 AM To: softimage@listproc.autodesk.com Subject: Difference between a force and a velocity ? Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained...
RE: Difference between a force and a velocity ?
Yes it's important because there are many equations which rely on velocity as a variable, not speed. If you're computing a speed, you need to accumulate the distance travelled over time. If you're computing a velocity, you're working with deltas. In more explicit terms, if you're computing motion vectors, you're comparing the current frame to the previous frame. If you're computing speed, you're comparing the current frame to the first frame. How you code for those scenarios is vastly different. Matt From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 11:58 AM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? is that distinctions helpful here? i mean we aren't just going to render the last frame of our particle going around the track, we are going to render 1440 frames (24fps*60secs) and at each frame the instantaneous velocity is going to have some direction and magnitude. On Wed, Feb 13, 2013 at 11:13 AM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: Velocity = net displacement / time. Force = Mass * Acceleration NOTE: Speed and velocity are very different. Speed is distance traveled over time (scalar) Velocity is net displacement over time (vector) Example: Running around a track in a stadium. If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position. Matt -Original Message- From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com] On Behalf Of olivier jeannel Sent: Wednesday, February 13, 2013 1:50 AM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Difference between a force and a velocity ? Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained...
Re: Difference between a force and a velocity ?
Even then, we are not computing the displacement between the first and the last frame only (which, of course, will lead to the wrongful observation that no displacement has taken place yielding zero velocity). In this case the displacement at the last frame will be calculated between the last and the second last frame. I think what Steven is saying makes sense. On 13/02/2013 3:03 PM, Matt Lind wrote: Yes its important because there are many equations which rely on velocity as a variable, not speed. If youre computing a speed, you need to accumulate the distance travelled over time. If youre computing a velocity, youre working with deltas. In more explicit terms, if youre computing motion vectors, youre comparing the current frame to the previous frame. If youre computing speed, youre comparing the current frame to the first frame. How you code for those scenarios is vastly different. Matt
Re: Difference between a force and a velocity ?
I think we get zero velocity only if we integrate it over elapsed time ( and it is not an instant vel which is used most of time I guess ), otherwise speed = scalar magnitude (length) of velocity, and the velocity = diff between the last and the prelast positions
Re: Difference between a force and a velocity ?
i know velocity is a delta and i have used it many a time as part of an equation which is variable. while your distinction is accurate i was concerned it wasn't helping olivier with that example which illustrates no displacement. i just dont think it was an intuitive example of velocity. in your example it would mean you sat in the bleachers to watch the race but left right before it starts and returned the moment it ends. so you say to your friend, man these guys haven't moved an inch! and she looks at you weird... On Wed, Feb 13, 2013 at 12:03 PM, Matt Lind ml...@carbinestudios.comwrote: Yes it’s important because there are many equations which rely on velocity as a variable, not speed. ** ** If you’re computing a speed, you need to accumulate the distance travelled over time. If you’re computing a velocity, you’re working with deltas.*** * ** ** In more explicit terms, if you’re computing motion vectors, you’re comparing the current frame to the previous frame. If you’re computing speed, you’re comparing the current frame to the first frame. How you code for those scenarios is vastly different. ** ** ** ** Matt ** ** ** ** ** ** *From:* softimage-boun...@listproc.autodesk.com [mailto: softimage-boun...@listproc.autodesk.com] *On Behalf Of *Steven Caron *Sent:* Wednesday, February 13, 2013 11:58 AM *To:* softimage@listproc.autodesk.com *Subject:* Re: Difference between a force and a velocity ? ** ** is that distinctions helpful here? ** ** i mean we aren't just going to render the last frame of our particle going around the track, we are going to render 1440 frames (24fps*60secs) and at each frame the instantaneous velocity is going to have some direction and magnitude. ** ** On Wed, Feb 13, 2013 at 11:13 AM, Matt Lind ml...@carbinestudios.com wrote: Velocity = net displacement / time. Force = Mass * Acceleration NOTE: Speed and velocity are very different. Speed is distance traveled over time (scalar) Velocity is net displacement over time (vector) Example: Running around a track in a stadium. If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position. Matt -Original Message- From: softimage-boun...@listproc.autodesk.com [mailto: softimage-boun...@listproc.autodesk.com] On Behalf Of olivier jeannel Sent: Wednesday, February 13, 2013 1:50 AM To: softimage@listproc.autodesk.com Subject: Difference between a force and a velocity ? Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained... ** **
RE: Difference between a force and a velocity ?
If you have a problem with the definitions, talk to mathematicians and physicists. I only put out the information for clarity as confusing speed with velocity is very common and there are times when it does indeed matter. Matt From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 12:47 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? i know velocity is a delta and i have used it many a time as part of an equation which is variable. while your distinction is accurate i was concerned it wasn't helping olivier with that example which illustrates no displacement. i just dont think it was an intuitive example of velocity. in your example it would mean you sat in the bleachers to watch the race but left right before it starts and returned the moment it ends. so you say to your friend, man these guys haven't moved an inch! and she looks at you weird... On Wed, Feb 13, 2013 at 12:03 PM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: Yes it's important because there are many equations which rely on velocity as a variable, not speed. If you're computing a speed, you need to accumulate the distance travelled over time. If you're computing a velocity, you're working with deltas. In more explicit terms, if you're computing motion vectors, you're comparing the current frame to the previous frame. If you're computing speed, you're comparing the current frame to the first frame. How you code for those scenarios is vastly different. Matt From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 11:58 AM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? is that distinctions helpful here? i mean we aren't just going to render the last frame of our particle going around the track, we are going to render 1440 frames (24fps*60secs) and at each frame the instantaneous velocity is going to have some direction and magnitude. On Wed, Feb 13, 2013 at 11:13 AM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: Velocity = net displacement / time. Force = Mass * Acceleration NOTE: Speed and velocity are very different. Speed is distance traveled over time (scalar) Velocity is net displacement over time (vector) Example: Running around a track in a stadium. If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position. Matt -Original Message- From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com] On Behalf Of olivier jeannel Sent: Wednesday, February 13, 2013 1:50 AM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Difference between a force and a velocity ? Hi list, Asking this question with no shame ^^; This might be basic, but what is the difference between a force and a velocity ? Sorry for being half brained...
Re: Difference between a force and a velocity ?
I'm a big fan of sticking to definitions, but they normally need to be presented in sets to the uninitiated, or they become confusing. IE: if you decide to put forward an example sampled across 6.6 seconds resulting in the case of no velocity despite much distance covered, the concept of discrete units and sampling intervals might need mentioning. It's probably easier to go Lagrangian, and assume the 1fps sampling unit, and examplify on that, if you don't want to touch on calculus (which I find tends to be more intimidating than most other fundamentals for new comers).
Re: Difference between a force and a velocity ?
i have no problem with the definitions and i just thought you might actually be causing more confusion with your example. On Wed, Feb 13, 2013 at 1:32 PM, Matt Lind ml...@carbinestudios.com wrote: If you have a problem with the definitions, talk to mathematicians and physicists. ** ** I only put out the information for clarity as confusing speed with velocity is very common and there are times when it does indeed matter.*** * **
RE: Difference between a force and a velocity ?
I gave the same definition and example as was used when I learned it in physics class all those years ago. I don't recall anybody having a problem with it then. Matt From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 1:46 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? i have no problem with the definitions and i just thought you might actually be causing more confusion with your example. On Wed, Feb 13, 2013 at 1:32 PM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: If you have a problem with the definitions, talk to mathematicians and physicists. I only put out the information for clarity as confusing speed with velocity is very common and there are times when it does indeed matter.
Re: Difference between a force and a velocity ?
Let me make somethings very clear here for the sake of discussion: Here we have to define whether or not we are talking of instantaneous velocity or simply velocity. As Raff touched the topic of Calculus (and also in almost all cases of studying the Newtonian Model of Classical Mechanics), most of the time we are dealing with instantaneous velocity, which as the name suggest, is the velocity of the object at the instant of time. In case the object starts and ends at the same point, once it has come to rest, both it's velocity and speed are zero. But just before that (and here comes deltas) at a moment of time it was not at the same place (it couldn't be as it is moving in some direction) and thus it will have velocity. Now consider a man walking on the tread mill, does he have velocity (or speed)? Neither because there is no displacement (huh ? the odometer is lying and I am sweating for nothin'). We always need to consider instantaneous stuff. Specially in our field it is of utmost importance as we are dealing with simulation and particles. Off topic, just for fun - Go read Zeno's Achilles and tortoise paradox (if you haven't already), which is somewhat related. You'll have fun ! On 13/02/2013 4:32 PM, Matt Lind wrote: If you make a complete lap in 60 seconds, then your speed is 6.66 meters per second, while your velocity is 0 meters per second because you haven't been displaced from your starting position.
RE: Difference between a force and a velocity ?
I think its other people who are blowing this out of proportion. After sending my initial email on the subject, I encountered this one from Olivier which precedes mine: Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time Seeing how I didn't do much differently than Caesar as far as explanation other than to give an example, I don't think I've done anything to split hairs or mislead people. I gave a very introductory explanation as is normally given on the 1st or 2nd day of a physics course. If you want to dive deeper and differentiate between instantaneous velocities and whatever everybody else is throwing about, then you are the ones splitting the hairs, not me. Matt From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Ed Manning Sent: Wednesday, February 13, 2013 2:05 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? C'mon, Matt -- You're sounding a little like Chris Cox here... ;-) You may be technically correct, but if we are going to split hairs, then we could also differentiate between net or average velocity, which you describe, and instantaneous velocity. (If I could figure out how to print proper equations and math symbols in email, then I'd probably go ahead and make a fool of myself trying to demonstrate my memory of 35-year old pre-calculus courses.) Anyway, change in position over change in time isn't really what I remember calling velocity in physics or math class -- velocity is the *limit* of change in position over change in time, as the amount of change in time nears zero. Or we could just say it's the derivative of position with respect to time, but then we need more definitions, which might mean more disagreements... Suffice to say that you can of course have any number of velocity vectors sum to zero over time. What might be more helpful to the OP would be using your example to introduce the concept of temporal sampling. Velocity isn't necessarily position now minus position a frame ago, even in an animation application -- it can be computed over any time interval, including subframe steps. And of course your example also illustrates temporal aliasing -- it's easy to miss important changes when you only look once every frame. When we compute motion vectors, we usually try to temporally subsample for exactly this reason. On Wed, Feb 13, 2013 at 4:32 PM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: If you have a problem with the definitions, talk to mathematicians and physicists. I only put out the information for clarity as confusing speed with velocity is very common and there are times when it does indeed matter. Matt From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 12:47 PM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? i know velocity is a delta and i have used it many a time as part of an equation which is variable. while your distinction is accurate i was concerned it wasn't helping olivier with that example which illustrates no displacement. i just dont think it was an intuitive example of velocity. in your example it would mean you sat in the bleachers to watch the race but left right before it starts and returned the moment it ends. so you say to your friend, man these guys haven't moved an inch! and she looks at you weird... On Wed, Feb 13, 2013 at 12:03 PM, Matt Lind ml...@carbinestudios.commailto:ml...@carbinestudios.com wrote: Yes it's important because there are many equations which rely on velocity as a variable, not speed. If you're computing a speed, you need to accumulate the distance travelled over time. If you're computing a velocity, you're working with deltas. In more explicit terms, if you're computing motion vectors, you're comparing the current frame to the previous frame. If you're computing speed, you're comparing the current frame to the first frame. How you code for those scenarios is vastly different. Matt From: softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.commailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Steven Caron Sent: Wednesday, February 13, 2013 11:58 AM To: softimage@listproc.autodesk.commailto:softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? is that distinctions helpful here? i mean we aren't just going to render the last
Re: Difference between a force and a velocity ?
... It was clearer before ... :DDD Le 13/02/2013 23:17, Matt Lind a écrit : I think its other people who are blowing this out of proportion. After sending my initial email on the subject, I encountered this one from Olivier which precedes mine: Thank's César ! Now it's clear :) Le 13/02/2013 11:13, César Sáez a écrit : They are completely different concepts, in short: Force = mass * acceleration Acceleration = Velocity / time Velocity = distance-traveled / time Seeing how I didn't do much differently than Caesar as far as explanation other than to give an example, I don't think I've done anything to split hairs or mislead people. I gave a very introductory explanation as is normally given on the 1^st or 2^nd day of a physics course. If you want to dive deeper and differentiate between instantaneous velocities and whatever everybody else is throwing about, then you are the ones splitting the hairs, not me. Matt *From:*softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] *On Behalf Of *Ed Manning *Sent:* Wednesday, February 13, 2013 2:05 PM *To:* softimage@listproc.autodesk.com *Subject:* Re: Difference between a force and a velocity ? C'mon, Matt -- You're sounding a little like Chris Cox here... ;-) You may be technically correct, but if we are going to split hairs, then we could also differentiate between net or average velocity, which you describe, and instantaneous velocity. (If I could figure out how to print proper equations and math symbols in email, then I'd probably go ahead and make a fool of myself trying to demonstrate my memory of 35-year old pre-calculus courses.) Anyway, change in position over change in time isn't really what I remember calling velocity in physics or math class -- velocity is the *limit* of change in position over change in time, as the amount of change in time nears zero. Or we could just say it's the derivative of position with respect to time, but then we need more definitions, which might mean more disagreements... Suffice to say that you can of course have any number of velocity vectors sum to zero over time. What might be more helpful to the OP would be using your example to introduce the concept of temporal sampling. Velocity isn't necessarily position now minus position a frame ago, even in an animation application -- it can be computed over any time interval, including subframe steps. And of course your example also illustrates temporal aliasing -- it's easy to miss important changes when you only look once every frame. When we compute motion vectors, we usually try to temporally subsample for exactly this reason. On Wed, Feb 13, 2013 at 4:32 PM, Matt Lind ml...@carbinestudios.com mailto:ml...@carbinestudios.com wrote: If you have a problem with the definitions, talk to mathematicians and physicists. I only put out the information for clarity as confusing speed with velocity is very common and there are times when it does indeed matter. Matt *From:*softimage-boun...@listproc.autodesk.com mailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com mailto:softimage-boun...@listproc.autodesk.com] *On Behalf Of *Steven Caron *Sent:* Wednesday, February 13, 2013 12:47 PM *To:* softimage@listproc.autodesk.com mailto:softimage@listproc.autodesk.com *Subject:* Re: Difference between a force and a velocity ? i know velocity is a delta and i have used it many a time as part of an equation which is variable. while your distinction is accurate i was concerned it wasn't helping olivier with that example which illustrates no displacement. i just dont think it was an intuitive example of velocity. in your example it would mean you sat in the bleachers to watch the race but left right before it starts and returned the moment it ends. so you say to your friend, man these guys haven't moved an inch! and she looks at you weird... On Wed, Feb 13, 2013 at 12:03 PM, Matt Lind ml...@carbinestudios.com mailto:ml...@carbinestudios.com wrote: Yes it's important because there are many equations which rely on velocity as a variable, not speed. If you're computing a speed, you need to accumulate the distance travelled over time. If you're computing a velocity, you're working with deltas. In more explicit terms, if you're computing motion vectors, you're comparing the current frame to the previous frame. If you're computing speed, you're comparing the current frame to the first frame. How you code for those scenarios is vastly different. Matt *From:*softimage-boun...@listproc.autodesk.com mailto:softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com mailto:softimage-boun...@listproc.autodesk.com] *On Behalf Of *Steven Caron *Sent:* Wednesday, February 13, 2013 11:58 AM *To:* softimage@listproc.autodesk.com mailto:softimage@listproc.autodesk.com *Subject:* Re
Re: Difference between a force and a velocity ?
[image: Inline image 1] On Thu, Feb 14, 2013 at 9:43 AM, olivier jeannel olivier.jean...@noos.fr wrote: ... It was clearer before ... :DDD physics.jpg
Re: Difference between a force and a velocity ?
please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote:
Re: Difference between a force and a velocity ?
I don't have an account, please feel free to do so in my place. I googled it though, didn't do all the post myself ;) On Thu, Feb 14, 2013 at 10:24 AM, Steven Caron car...@gmail.com wrote: please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
The example of running around on a track is wrong unless you're on a stationary planet. Way to confuse Olivier, guys :( Here's my stab: Definitions aside, velocity describes how something is moving at an instant in time. Force, however, is more closely related to how an object will accelerate over time (in that the acceleration of the object is directly proportional to the forces acting upon it). So if a force is acting on an object, that will cause it to start moving differently as time passes, like what happens when you drop something. When you drop a ball, gravity (a force) causes its downward velocity to increase more and more as time passes. A noteworthy exception to this simple explanation of forces and velocity are forces that are actually dependent on velocity. In practice, one of the most common such forces is the force of friction with a surface, such as a table top (or even the surface of air against the object, which is a component of the drag force affecting an object traveling through a medium). For example, as an object travels faster and faster through the air, the force of friction with the air will increase. This is why when you first drop a ball it speeds up on its way down, but once it's falling fast enough, it will stop speeding up and continue at a constant speed (and constant velocity, if you're a stickler for terminology). Once the ball is falling at a fixed speed, you know that the force of gravity and the force of drag/friction are equal and opposite, such that they cancel out. This is of course ignoring secondary effects, such as the heat generated by the people below arguing over email forums about how physics works. In this case, as the arguing increases, the amount of hot air released increases, and the air surrounding the ball becomes thinner, reducing the drag force on the ball, and causing it to fall even faster, thereby increasing the speed at which the ball hits its intended target, hopefully reminding that target that it's silly to get worked up over Newtonian physics, since it's a simplified approximation of reality anyway. - Andy On Wed, Feb 13, 2013 at 3:54 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: I don't have an account, please feel free to do so in my place. I googled it though, didn't do all the post myself ;) On Thu, Feb 14, 2013 at 10:24 AM, Steven Caron car...@gmail.com wrote: please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote: -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
But is the ball propelled by an internal combustion engine, or is it victim of the gravitational pull? Because if it's the former I feel it's remiss of you to forget that cold air is more compressible (or rather more easily pulled in larger quantities) than hot air, and therefore results in a more favorable stoichiometric ratio chambered and more power. Seriously, man, get your examples right! You can't omit details like that. On Thu, Feb 14, 2013 at 1:08 PM, Andy Jones andy.jo...@gmail.com wrote: The example of running around on a track is wrong unless you're on a stationary planet. Way to confuse Olivier, guys :( Here's my stab: Definitions aside, velocity describes how something is moving at an instant in time. Force, however, is more closely related to how an object will accelerate over time (in that the acceleration of the object is directly proportional to the forces acting upon it). So if a force is acting on an object, that will cause it to start moving differently as time passes, like what happens when you drop something. When you drop a ball, gravity (a force) causes its downward velocity to increase more and more as time passes. A noteworthy exception to this simple explanation of forces and velocity are forces that are actually dependent on velocity. In practice, one of the most common such forces is the force of friction with a surface, such as a table top (or even the surface of air against the object, which is a component of the drag force affecting an object traveling through a medium). For example, as an object travels faster and faster through the air, the force of friction with the air will increase. This is why when you first drop a ball it speeds up on its way down, but once it's falling fast enough, it will stop speeding up and continue at a constant speed (and constant velocity, if you're a stickler for terminology). Once the ball is falling at a fixed speed, you know that the force of gravity and the force of drag/friction are equal and opposite, such that they cancel out. This is of course ignoring secondary effects, such as the heat generated by the people below arguing over email forums about how physics works. In this case, as the arguing increases, the amount of hot air released increases, and the air surrounding the ball becomes thinner, reducing the drag force on the ball, and causing it to fall even faster, thereby increasing the speed at which the ball hits its intended target, hopefully reminding that target that it's silly to get worked up over Newtonian physics, since it's a simplified approximation of reality anyway. - Andy
RE: Difference between a force and a velocity ?
There's nothing wrong with the running track example. You are overthinking the problem. It's an introductory level illustration to clarify the difference between speed (scalar) and velocity (vector), and is used in physics text books believe it or not. If you do a google search on physics definition of velocity, the top three results all explain velocity as the change in position divided by the change in time. (e.g. v = x1 - x0 / t1 - t0). If the start position and end position are the same, then the velocity is indeed zero over any time interval because it has no magnitude, and proven mathematically. If you have a problem with that, take it up with the physicists and mathematicians. From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Andy Jones Sent: Wednesday, February 13, 2013 6:08 PM To: softimage@listproc.autodesk.com Subject: Re: Difference between a force and a velocity ? The example of running around on a track is wrong unless you're on a stationary planet. Way to confuse Olivier, guys :( Here's my stab: Definitions aside, velocity describes how something is moving at an instant in time. Force, however, is more closely related to how an object will accelerate over time (in that the acceleration of the object is directly proportional to the forces acting upon it). So if a force is acting on an object, that will cause it to start moving differently as time passes, like what happens when you drop something. When you drop a ball, gravity (a force) causes its downward velocity to increase more and more as time passes. A noteworthy exception to this simple explanation of forces and velocity are forces that are actually dependent on velocity. In practice, one of the most common such forces is the force of friction with a surface, such as a table top (or even the surface of air against the object, which is a component of the drag force affecting an object traveling through a medium). For example, as an object travels faster and faster through the air, the force of friction with the air will increase. This is why when you first drop a ball it speeds up on its way down, but once it's falling fast enough, it will stop speeding up and continue at a constant speed (and constant velocity, if you're a stickler for terminology). Once the ball is falling at a fixed speed, you know that the force of gravity and the force of drag/friction are equal and opposite, such that they cancel out. This is of course ignoring secondary effects, such as the heat generated by the people below arguing over email forums about how physics works. In this case, as the arguing increases, the amount of hot air released increases, and the air surrounding the ball becomes thinner, reducing the drag force on the ball, and causing it to fall even faster, thereby increasing the speed at which the ball hits its intended target, hopefully reminding that target that it's silly to get worked up over Newtonian physics, since it's a simplified approximation of reality anyway. - Andy On Wed, Feb 13, 2013 at 3:54 PM, Raffaele Fragapane raffsxsil...@googlemail.commailto:raffsxsil...@googlemail.com wrote: I don't have an account, please feel free to do so in my place. I googled it though, didn't do all the post myself ;) On Thu, Feb 14, 2013 at 10:24 AM, Steven Caron car...@gmail.commailto:car...@gmail.com wrote: please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.commailto:raffsxsil...@googlemail.com wrote: -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Difference between a force and a velocity ?
Since this whole convo is about velocity, I feel the 1st What If is more relevant: http://what-if.xkcd.com/1/ Teaser: baseball, 90% speed of light and doom. On Wed, Feb 13, 2013 at 11:08 PM, Xavier Lapointe xl.mailingl...@gmail.comwrote: http://what-if.xkcd.com/28/ Teaser: Physics, Steaks, and Cooking. On Thu, Feb 14, 2013 at 3:01 PM, Andy Jones andy.jo...@gmail.com wrote: http://xkcd.com/1145/ On Wed, Feb 13, 2013 at 7:12 PM, Eric Thivierge ethivie...@gmail.comwrote: Can someone explain this Physics thing to me? Eric Thivierge http://www.ethivierge.com -- Xavier
Re: Difference between a force and a velocity ?
Added. ;) On Wed, Feb 13, 2013 at 6:24 PM, Steven Caron car...@gmail.com wrote: please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote:
Re: Difference between a force and a velocity ?
wow... On Wed, Feb 13, 2013 at 10:39 PM, Alan Fregtman alan.fregt...@gmail.comwrote: Added. ;) On Wed, Feb 13, 2013 at 6:24 PM, Steven Caron car...@gmail.com wrote: please add... http://cgmemes.blogspot.com/ On Wed, Feb 13, 2013 at 3:01 PM, Raffaele Fragapane raffsxsil...@googlemail.com wrote:
