Holy moley, what I started by just telling the doctor that I "weighed" 104 kg ...
Carleton -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of James Frysinger Sent: Monday, January 26, 2009 14:36 To: U.S. Metric Association Subject: [USMA:42607] Re: The real physics (was Small item seen on TV) Thank you, Gene. But I continue to disagree with you. You state, "There is no pull on the orbiter by the weight of the orbiter, which is tangential to the path of the orbiter!" That is patently false. The orbiter's weight vector points from the orbiter towards the center of mass of the Earth (essentially perpendicular to the orbiter's near-circular path). The weight vector is not tangential to the orbiter's path. I know that you worked with NASA in earlier days. As I've said, NASA is fond of spacecraft-centric frames of reference. It simplifies many of the engineering calculations they make. It also confounds the physics of the situation. Recall, these are the folks who created the slinch. That view, of course, fails to explain what keeps orbiting bodies from traveling off into space in a straight line (per Newton's first law of motion, Galileo's principle of inertia) and instead accelerates them into elliptical orbits. Acceleration is the rate of change in velocity, which implies a change in speed, direction, or both. This requires the application of an unbalanced external force --- Newton's second law of motion. Centripetal acceleration is not a "magic event". Jim [email protected] wrote: > Jim, > > Ah! But your classic physics is in error as detailed below for the approximate inertial frame with origin at the center of the earth. There is no pull on the orbiter by the weight of the orbiter, which is tangential to the path of the orbiter! Even the earth frame is non-inertial to some degree as the earth accelerates in its orbit about the sun. > > Certainly, the free falling elevator is more obviously a non-inertial frame. > > Inertial frames exist only in approximation when motions within the solar system, motion of the solar system within the milky way galaxy, motion of the milky way within its cluster, etc. are included in increasingly more cosmic cases. > > Gene. > > ---- Original message ---- >> Date: Mon, 26 Jan 2009 09:57:31 -0600 >> From: James Frysinger <[email protected]> >> Subject: [USMA:42600] Re: The real physics (was Small item seen on TV) >> To: "U.S. Metric Association" <[email protected]> >> >> >> Gene, >> >> You are using non-inertial reference frames, which can give rise to >> pseudoforces (such as centrifugal force). I know that NASA is fond of this. >> >> I'll stick by classical physics, thank you. >> >> Jim >> >> [email protected] wrote: >>> Jim, >>> >>> Here are several corrections of your statements. See below. >>> >>> ---- Original message ---- >>>> Date: Sun, 25 Jan 2009 18:38:55 -0600 >>>> From: James Frysinger <[email protected]> >>>> Subject: [USMA:42574] Re: The real physics (was Small item seen on TV) >>>> To: "U.S. Metric Association" <[email protected]> >>>> ... >>>> >>>> The astronauts orbiting the Earth are not weightless. >>> False. There weights are nearly zero with respect to their immediate surroundings. They are "weightless" in first approximation in the reference frame of their spacecraft. >>> >>>> Their gravitational weight is the centripetal force that pulls them around in orbit. >>> False. The central force accelerates them toward the center of the earth, but it is perpendicular to their direction of motion in the orbit. >>> >>>> Likewise, their orbiter's weight pulls it around in orbit. >>> False. There is no tangential pull (thrust) and little drag on the spacecraft in parking orbit. >>> >>>> ... >>> *With the earth as the frame of reference*: >>>> The weight of an object at Shuttle Orbiter altitudes is >roughly 92 % of its weight on the surface of the Earth. At >ISS altitudes it's roughly 91 %. >>> *With the orbiter as the frame of reference*: >>> >>>> ...the astronauts are in orbit with their orbiter and since >both experience the same centripetal acceleration, the >astronauts feel "weightless" and float around inside the >orbiter. >>>> >>>> A similar phenomenon can be experienced (briefly) in an >elevator whose cable has been cut... >>> I have no quibble with your elevator and other examples. >>> >>> Gene. >>> >>> >>> >> -- >> James R. Frysinger >> 632 Stony Point Mountain Road >> Doyle, TN 38559-3030 >> >> (C) 931.212.0267 >> (H) 931.657.3107 >> (F) 931.657.3108 >> > > > > -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
