On Mon, Dec 23, 2024 at 4:10 PM Alan Grayson <[email protected]> wrote:
> On Sunday, December 22, 2024 at 10:05:54 PM UTC-7 Jesse Mazer wrote: > > BTW, since you seem to be interested in a scenario where the car and > garage are exactly matched in length in the garage frame, something which > isn't true in Brent's scenario, here's a different scenario you could look > at, where I'm again using units where c=1, let's say nanoseconds for time > and light-nanoseconds (i.e. distance light travels in one nanosecond) for > distance. > > --Car's rest length is 25, garage's rest length is 20, car and garage have > a relative velocity of 0.6c, so gamma factor is 1/sqrt(1 - 0.6^2) = 1.25 > > > *OK. * > > > --In garage rest frame, garage has length 20 and car has length 25/1.25 = > 20. In the car rest frame, the garage has length 20/1.25 = 16 and the car > has length 25. > > > *OK, assuming car is moving, but I wouldn't call that "in the car rest > frame" since you have garage length as contracted. AG * > > BTW I forgot to reply to this line since it was an overall "OK", but just wanted to note that this is the standard meaning of "[object's] rest frame" in physics--it refers to the inertial coordinate system where the object, in this case the car, has position coordinates that don't change with coordinate time, so the car is said to be "at rest" in this coordinate system. It is the garage, not the car, that is moving in the car's rest frame, since the garage's coordinate position does change with time in this frame--this relative perspective on who is "moving" and who is "at rest" is just as true in classical mechanics as in special relativity (though of course there is no length contraction accompanying motion in classical mechanics), see the discussion of Galilean relativity at https://www.physicspace.com.ng/2018/09/galilean-relativity-2.html with Galileo's own discussion of an observer below decks of a windowless ship who has no way of knowing if the ship is at moving smoothly over the water or at rest relative to it. If you don't understand this sort of basic observation about classical mechanics in an inertial coordinate system (along with other basic observations like the classical relation between 'length' and coordinates of endpoints of an object, or classical relation between 'velocity' and the way position coordinates of an object change with coordinate time), that's something you really need to bone up on a little before tackling relativity. Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAPCWU3KjHCEAcg%3D15a4D2G1%3DW-SqgaAQ34%3Depg_cuSdnztewWQ%40mail.gmail.com.
