# Why are astronauts weightless?

#### Buckleymanor

No, the speed would not remain constant. It varies with the distance from the earth. As that distance increases, gravitational potential energy goes up and kinetic energy, and thus speed, goes down.
I don't understand how this can be true if speed changes.
If, on the other hand, you were moving horizontally near the earth, if the only force acting on you were gravity and if your speed were faster or slower than that which would put you in a circular orbit then you would still be in free fall. You would follow an elliptical, parabolic or hyperbolic trajectory.

But you would not feel any kind of weight.
If your speed changes then you accelerate and decelerate or vise versa how come you would not feel any kind of weight.

#### A.T.

If your speed changes then you accelerate and decelerate or vise versa how come you would not feel any kind of weight.
Read page 1 (post #4, #7). This thread is already repetitive enough.

#### p1l0t

I don't understand how this can be true if speed changes.

If your speed changes then you accelerate and decelerate or vise versa how come you would not feel any kind of weight.
I know where your coming from. W = kg is basically F = ma. I think it depends on the reference frame though. The astronaut may not feel any acceleration but relative to Earth he is.

#### Doc Al

Mentor
I don't understand how this can be true if speed changes.

If your speed changes then you accelerate and decelerate or vise versa how come you would not feel any kind of weight.
Please take A.T.'s advice and read this thread from the beginning. Acceleration does not matter as long as gravity is the only force acting.

#### Buckleymanor

Please take A.T.'s advice and read this thread from the beginning. Acceleration does not matter as long as gravity is the only force acting.
Sorry for the late reply but I could not get access to the beginning of the thread for some time.
From what I can gather acceleration does not matter as long as the object is small.
For example if you were to have a very large accelerometer travelling in an eliptical path around the Earth it would register gravitational changes.
So is the argument only about size.

#### A.T.

For example if you were to have a very large accelerometer travelling in an eliptical path around the Earth it would register gravitational changes.
I would't call it an accelerometer, but a tidometer.

#### sophiecentaur

Gold Member
Microgravity keeps popping up here and it has some significance for objects in orbit.
You could detect whether you were in orbit (significantly close to a large object) or just floating out in deep deep space because of the presence of microgravity whilst in orbit, which would reveal itself as detectable 'weight forces' by an accelerometer, for instance, placed on the innermost wall and outermost walls - a gradient of force across the width of the craft. The inner and outer parts of the craft will be going at the 'wrong' speeds to maintain a circular orbit (with a period which is only correct for the CM orbital radius) so there would be detectable 'outward' forces against the walls (and the equal and opposite reaction forces, of course).

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