# Astronauts & Human Centrifuges

1. Sep 4, 2014

### Jimmy87

Hi pf, please could someone explain how a human centrifuge enables astronauts to experience a simulated gravity effect. I understand that if a centrifuge machine has a centripetal acceleration of 20 m/s^2 then they will feel a force of 2g. The thing that confuses me is that they are spun on a horizontal plane so in the y-plane where gravity normally acts there is no centrifugal effect yet the astronauts on the human centrifuge find it difficult to lift their hand up (in the y-plane). Surely if your being spun on a horizontal plane you only feel the simulated gravitational effect across your body?

Also, if the human centrifuge goes too fast the person inside is at risk of dying apparently. I was just wondering what would actually kill you since there is no such thing as a centrifugal force. Would they be killed by the centripetal force pushing against them or by their inertia or both?

Thanks people!

2. Sep 4, 2014

### Bandersnatch

Newton's first law tells you an astronaut in the spinning centrifuge(i.e., with some tangential velocity) should move in a straight line unless a force acts on him/her. Where does the force that makes the path of motion curved to form a circle come from, and which direction is it acting? Can you compare the situation to a person standing on Earth?

Re: your second question. What do you think would kill a person if Earth's gravity would suddenly increase many times?

3. Sep 4, 2014

### A.T.

Acceleration is equivalent it gravity:

2g horizontally and 1g vertically if still on Earth. So more than 2g in total.

What is Y? Vertical to the ground, or vertical to the cabin, that aligns with the effective gravity (vector sum of Earth's gravity and centrifugal gravity)?

What kills you physiologically depends on many factors. But the general physical cause is the non-uniform application of forces to your body.

Last edited: Sep 4, 2014
4. Sep 4, 2014

### Jimmy87

What is Y? Vertical to the ground, or vertical to the cabin, that aligns with the effective gravity (vector sum of Earth's gravity and centrifugal gravity)?

Thanks for your answers guys! I mean y in the conventional sense if you were standing still on Earth, so vertically. The centrifuge you show in the picture isn't like the one I saw. The one I saw was and video where with cabin that the astronauts sit in that spins around horizontally. When they try to lift their hand up (vertically) in the cabin they can't when the g's build up but I don't understand why because the vertical g-force is still the same without being in the centrifuge as the centrifuge is not spinning in the vertical (y) plane?

5. Sep 4, 2014

### A.T.

It spins horizontally, but banks to align with the effective gravity.

6. Sep 4, 2014

### sophiecentaur

The type of centrifuge I have seen in films of Space Training had a much larger radius. This ensures that the simulated g force is more even, over the trainee's dimensions. The 'banking' can be achieved by just having the seat / cage on a gimbal , which would not involve the long arm leaving the horizontal plane.

7. Sep 4, 2014

### Jimmy87

Thanks to all. I managed to find the video () and yes you are right it is banked. I just didn't pick up on it as it only shows a view from the outside momentarily.

Last edited by a moderator: Sep 25, 2014
8. Sep 4, 2014

### A.T.

He would hardly sit so nicely straight with 5g sideways acceleration.

Last edited by a moderator: Sep 25, 2014
9. Sep 4, 2014

### Jimmy87

Good point indeed!