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 >
