osman@sprite.DEC (Eric, DIGITAL, Burlington Ma. 617 273-7484) (12/19/85)
I believe the key to the answer is the word "orbit". If you're in orbit, you're whizzing around the earth just fast enough so that your centrifical force OUTWARD matches gravity's force INWARD. Hence the total acceleration for you is zero, and hence you are indeed weightless. p.s. Does someone remember the details of the "thought" experiment involving being in a windowless elevator, and trying to determine whether you are accelerating or just plain heavy ?
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (12/21/85)
> p.s. Does someone remember the details of the "thought" experiment > involving being in a windowless elevator, and trying to determine > whether you are accelerating or just plain heavy ? Sure, what do you want to know? This example is used in almost every elementary explanation of the general theory of relativity.
tan@ihlpg.UUCP (Bill Tanenbaum) (12/24/85)
> [Eric] > I believe the key to the answer is the word "orbit". If you're in orbit, > you're whizzing around the earth just fast enough so that your centrifical > force OUTWARD matches gravity's force INWARD. > > Hence the total acceleration for you is zero, and hence you are indeed > weightless. ---------- Wrong. Zero acceleration and weightlessness are not the same thing! The only force on you is gravity [INWARD]. Your acceleration is not zero. That is why your trajectory is an ellipse and not a straight line. You are "weightless" because you are in free fall, i.e., not restrained by non-gravitational forces, just like you would be in the free falling elevator or airplane. You have "weight" on earth only because the non-gravitational contact force of the earth's surface prevents you from falling freely towards the center of the earth. Your total acceleration is zero, but you are NOT weightless. In other words, when you are in free fall, you are accelerating due to the local gravitational field. You are weightless because in YOUR OWN REFERENCE FRAME (not the fixed frame of the earth) there are no gravitational forces on you. When you are held back from free fall, as by the surface of the Earth, the gravitational force manifests itself as "weight". -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan