Re: summary of weight

[brian whatcott <inet@INTELLISYS.NET>]

At 23:39 10/16/99 -0400, you wrote:
> Can someone explain to me, as an observer fixed on
> the Earth's surface, why I cannot differentiate between
> a gravitational force and a force such as
> produced by an elevator?
>
> Bob Carlson

I'll take a shot at this.

If you step into an elevator whose frame is fixed to the Earth's
surface, something happens when you punch a button.
You get a minor jostle.

This is not what you have in mind. There is this 'fairy story'
 or gedanken experiment I should call it, that says that an elevator
that is constantly accelerating with respect to the Earth surface
provides an effect exactly like a change in gravity.

 But if you look out, you immediately see a difference.
So the elevator has to have opaque walls.

But if you arranged the elevator to accelerate
 downwards so as to complete cancel your weight, the things floating
 in the air around you would start to move together as they moved
 radially inwards towards Earth center.

This is after all, just a fairy story.
If it were a REAL experiment, the elevator shaft would
need to be thousands of feet deep, and the shaft would need to be
evacuated because of the mounting air pressure as speed rapidly
increases.

 Then you remember that as the elevator descends into the depths,
 you are rotating with the Earth, but less fast in tangential terms,
so these floating objects are not only floating towards each other,
 they are drifting towards the East.

You can easily see that the elevator story has its limitations....

So lets shift onto a rocketship, far in interstellar space, which is
accelerating at 9.7 m/s
Einstein persuaded physicists that they could not instrument
the rocket to indicate a distinctive difference between the effects
of acceleration, and the force that they feel to be pulling them down
to Earth.

He said this was because the accelerating rocket ship provides
an effect which acts on the inertial property of matter.
 Whereas the mass of the Earth provides an attractive effect on other
objects with mass. And these two effects give identical effects.
 Your question is simply, "why is this?"

Einstein's triumph was to say: the identity of effects is no accident:
they are the SAME effect - inertial acceleration - one caused by an
external force, the other caused by a strange effect that mass and
space have on each other that feels like acceleration to objects in
the vicinity.

And that is as far as I can stray into physicist territory on this one.


brian whatcott <inet@intellisys.net>
Altus OK