Re: [Phys-l] Space Balloon

[Brian Whatcott <betwys1@sbcglobal.net>]

At 05:17 PM 2/20/2007, Paul Giusti, you wrote:

> I ..feel the urge to think out loud in the hope that my confusion can be
> clarified!
>
> Firstly, in relation to this "equivalence principle", I cannot see how it
> could be stated that if the spacecraft/car accelerates toward the "front",
> then the balloon would also move to the "front".
> The reason for my confusion on this one is that if the vehicle is moving
> forward, the balloon should not travel in the same direction- it should
> travel in the opposite direction- towards the "back".
>
> If you stood in a bus and the bus accelerated forward, you are going to move
> in the opposite direction. No?
>
> Secondly, if it is a helium balloon, would it not travel upwards?

In my always humble view, John D's comparison
of a helium balloon in an orbiting spacecraft, (which is always
accelerating downwards) with a tethered helium balloon in a
 car which accelerates in the direction parallel to the road
surface is not a perfectly useful analogy here.

Still,  I should at least mention, in case the observation
 has escaped Paul Giusti,  that a tethered helium balloon in a
 car speeding up in the forwards direction does indeed
 move forwards on its tether, just as a blob of water
 hovering in an orbiting spacecraft would move backwards
if the spacecraft accelerated in the forward direction.

It is necessary only to point to observational results for
 confirmation.
Helium balloons are not expensive!


Brian Whatcott    Altus OK    Eureka!