# Experiments in a revolving satellite

## Main Question or Discussion Point

A revolving satellite is similar to a lift which is falling from a height. Only the difference is that the satellite has a very high horizontal velocity due to which the satellite moves forward while falling to earth. And when the earth's curvature and the lift's downfall match, the satellite keeps revolving. Like in a freely falling lift, a man inside the satellite does not feel the gravity and his apparent weight is zero. Now when we conduct an experiment in the satellite what equations/formulas do we use? How do the expermients in satellite compare with the same on the earth? For example, when we conduct experiments of surface tension (capillary tubes), what do we use in the formula for the parameter gravity - the gravity that is really working in the satellite or the apparent gravity i,e. zero?

## Answers and Replies

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If the man inside the satellite experiences zero gravity than that means all forces acting on him cancel each other out, in other words it is as good as if they didn't exist. Thus you will use normal equations but gravity will be equal to zero.

But satellite is accelerating i.e. it is atleast changing the direction. In an accelerating frame, the physics laws hold good?

But satellite is accelerating i.e. it is atleast changing the direction. In an accelerating frame, the physics laws hold good?
Be careful. You have non-inertial reference frame (because it's accelerating). Because of that, inertial (fictitious) force appears. It can cancel the gravity if it has the opposite direction and equal magnitude. Otherwise, the net force will be different.

So, it's obvious that some things will not be same in such conditions. Let's say that you have a balloon with air in it. If you put it in water it will not get back to the surface. There is no lift because there is no difference in hydrostatic pressures. $$p=p_{0} + \rho g h$$. Since g=0, $$p=p_{0}$$. $$p_{0}$$ is the pressure outside of the water (or some other fluid).

But satellite is accelerating i.e. it is atleast changing the direction. In an accelerating frame, the physics laws hold good?
Imagine the satellite is a stone thrown at 45 degrees
It's trajectory will be a nice parabola (ignoring air resistance) But everything inside that stone (or satellite) experiences weightlessness as it goes. It is in fact completely equivalent to the weightlessness inside of a satellite in orbit above the Earth.

When you jump into the air you experience zero g the whole time.
(for about a second or two .)

Regardless of whether your motion is actually upward or downward you always feel the weightlessness.
Remember : when you jump upwards you are falling up for a short while
Then you start to fall back down.
Your acceleration is constant and is the same throughout.

edit: ..erm,
What I was trying to say is that you can completely ignore the effects of gravity inside the satellite.
Just as Nerd had said in post #2

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weightlessness - a feeling.

What is this feeling of weight and weightlessness? When you are free falling, gravitation is working on you. You should feel the force, but you don't feel it. You feel weightlessness when you are free falling. Why do we feel this way, we feel "weightless" when a force is acting on us?

The feeling of weightlessness is simply the fact that you cannot detect the pull of gravity on your arms legs - any part of you for that matter. All you senses of touch and push/pull tell you that you are basically floating in space (disregarding air resistance of course which can give the game away)

In fact the only way you know you are moving at all is because you can see the ground coming back up toward you. But seeing is not quite the same as feeling is it. If you were a blind man you could be completely fooled into thinkig you were floating with no acceleration whatsoever. Until you hit the ground.