What am I feeling on a roller coaster?

[AaronX]

@Francis_Vaughan

Not really.

If you are in freefall there is no apparent acceleration that you can feel. If you were in a box and could not see outside you could not tell the difference between being in zero gravity or in freefall. This is one of the key points of physics.

When you reach terminal velocity you cease to accelerate - so you feel the full force of gravity. It is only whilst you are accelerating up to terminal velocity that you feel weightless, or feel as if you have less weight.

This is counter-intuitive I know.

The vomit comet dives in an as close a trajectory as it can to free fall in order to get weightlessness for the passengers. It needs power to overcome aerodynamic drag on the way down, and to keep accelerating down. It is only while it is accelerating downwards that the passengers feel weightless. When it runs out of either height or reaches its maximum safe speed it must slow down, and weightlessness vanishes.

Hey, come to think of it, you’re right. That means the vomit comet must continue accelerating at G, past terminal velocity, to maintain weightlessness.

Basically, constant speed (including terminal velocity) means you feel your weight. Either by your feet supporting it, or your back on a bed, or your back supported by air. Accelerating at G towards the centre of Earth means you feel weightless. In orbit, this acceleration is “used” to make you travel in a circle, so you don’t change speed, only direction. If you had a marble in a container, and moved the container so that the marble didn’t touch the sides, the marble would feel weightless.