artificial gravity / spinning space craft.

[ColJack]

here's one for the science guys and the SciFi geeks as well..

we've all seen one show / film or another at some point where they use a spinning section of a space station or craft to create "artificial gravity" for the occupants.
we all know that this is just certifugal force and not real gravity.

now if I were standing on the inner surface of a space station and jumped hard enough in the opposite direction to the rotation, would I then be able to float a few inches above the spining surface? ( barring anything fixed to the surface colliding with me of course... )

the surface would be rushing past me obviously but I would be weightless yes?

 

[Johnmelad502]

here's one for the science guys and the SciFi geeks as well..

we've all seen one show / film or another at some point where they use a spinning section of a space station or craft to create "artificial gravity" for the occupants.
we all know that this is just certifugal force and not real gravity.

now if I were standing on the inner surface of a space station and jumped hard enough in the opposite direction to the rotation, would I then be able to float a few inches above the spining surface? ( barring anything fixed to the surface colliding with me of course... )

the surface would be rushing past me obviously but I would be weightless yes?

 

[joe-90]

It's not centrifugal force at all, it's all about the deformation of space/time. Thus it is real gravity.

 

[joinerjohn]

If you pushed hard enough, you'd experience weightlessness. Remember that as soon as your feet leave the floor your body is trying to move in a straight line (at a tangent to the centre of rotation) Therefore your body would tend to move back towards the floor. Being as it's circular)
The mathematics for this is rather complicated so I won't bore you with the details.
Suffice to say that in the scenario where your in a rotating space station, rather like the "Rotor " rides at a fairground, your body ( when in contact with the floor) is actually trying to move in a straight line, but the floor prevents this and so you perceive a gravity effect.
If the space station is orbiting the Earth, you also have to take into account, the orbital velocity of the station itself, or if travelling to another planet, you have to take the forward velocity of the station into account.
In effect it's all relative to the person on the station experiencing the various forces acting upon that persons body. You would perceive gravity, although none is involved.

Hope this helps .

 

[joe-90]

Stick to joinery eh john.

 

[Donkmeister]

I've never actually thought about this before, despite a previous life as a physicist I always take it as read in sci-fi films that spinning spaceships stop you flying away!

But, considering the forces at work, it's all to do with centripetal force. You are standing there on the floor of your space station, your body wants to continue travelling in whatever direction it is going. If the space station is spinning, your body wants to fly in a straight line, i.e. straight off at a tangent to the space station.

However, the floor of the space station stops you doing that, and instead your momentum remains as angular momentum.

Jumping upwards would not stop you falling back down. Jumping really hard would result in you falling onto the opposite floor (assuming a big hollow spacecraft with no ceilings). If you could judge it perfectly, you could end up at the central point, however that would be an unstable equilibrium and the next time you exhaled you would unsettle that equilibrium and fall.

To try and visualise it, imagine you have a conker on a string and are swinging it around your head. If you let go, it will fly off in a straight line. The string is transmitting the force that keeps the conker travelling in a circle, but on the space station this would be provided by the floor.

 

[Donkmeister]

Stick to joinery eh john.

Speaking as a former physicist I'd say he's got it spot on.

 

[joe-90]

Why does a bicycle wheel not fall over when rolled at 5 mph? You are the physicist.

 

[joinerjohn]

Why does a bicycle wheel not fall over when rolled at 5 mph? You are the physicist.

Quite simple Joe,, The wheel is acting as a gyroscope. Once the wheel is spinning , it tends to try to stay in the same plane that it started spinning in (Newtons Laws of Motion in action).
Here's an experiment for you to try at home.
Take a bicycle wheel and hold it by the axle with both hands straight out in front of you. Ask someone to set it spinning, then try and rotate your body to the right whilst trying to keep the bicycle wheel upright.
It's almost impossible to keep the wheel upright, because your trying to change the plane in which it started spinning. Were it spinning fast enough, you'd lose hold of the axle.


BTW in the original scenario with a space station/craft utilising a spinning section to provide gravity. When travelling to another planet, course changes would involve very very complicated mathematics . Simply because the spinning section would also act as a gyroscope and try to stay spinning in the same plane it started in.

 

[ColJack]

but that's my point Donk, there is no up and down in space, it's only your velocity and centrifugal force keeping you pinned to the wall of the spinning bit.

once you leave the floor, if you manage to cancel your centrifugal force ( if, say you run as fast as the spinning bit is spinning in the opposite direction and then jump a little ), you become weightless again..

or if looked at from another perspective, if you start at the center of the big spinning drum and manouver yourself towards the outside wall, you're still weightless and stationary in space ( a hypothetical space station in the middle of nowhere with a directional speed of 0, ie at a fixed point in space, not moving anywhere.. )
until you actually contact the wall and start spinning with it then you could be a hairs width from it and still be weightless..

as an analogy think of a washing machine, if you were to have no door on it and held a conker in the center and lowered it towards the spinning drum then ( ignoring regular earth gravity ) the conker wouldn't experience any outward force or tendency to stick to the inner wall of the drum just by the drum simply spinning.

or lets take John's "rotor ride" scenario..
lets asume it's open top and is fixed in position ( ie not a "tilt a whirl" type that pivots and moves the point of rotation ).
once it's spinning, you are lowered down into it from above by a crane and harness. until you touch the wall and start to spin with it you could be inches away from the wall and not feel the "g-gorce" that people pinned to the wall would be feeling..

 

[Blasphemous]

Why does a bicycle wheel not fall over when rolled at 5 mph? You are the physicist.

Because it's attached to a bike that someone is riding....?

 

[joinerjohn]

Coljack, in your second scenario with the space station at 0 velocity, but the section spinning. If you started at the centre of the spinning section and floated gently towards the spinning section,,, Yes when you were a few inches off that section, you'd see it spinning below your feet..... However,,,,,,, Once you actually touched the spinning section and accelerated to the speed of that section, then physics dictate that your body would now be trying to travel in a straight line. Only the floor/ side of the spinning section would prevent that. It would take either a super computer or extreme luck for you to ever become weightless again by simply pushing yourself off the floor/side of the space station.

 

[ColJack]

Coljack, in your second scenario with the space station at 0 velocity, but the section spinning. If you started at the centre of the spinning section and floated gently towards the spinning section,,, Yes when you were a few inches off that section, you'd see it spinning below your feet..... However,,,,,,, Once you actually touched the spinning section and accelerated to the speed of that section, then physics dictate that your body would now be trying to travel in a straight line. Only the floor/ side of the spinning section would prevent that. It would take either a super computer or extreme luck for you to ever become weightless again by simply pushing yourself off the floor/side of the space station.

then lets asume that I have a bike with me and pedal in the oposite direction just as fast as the station spins, effectively cancelling my rotational velocity.

as I rode faster on the bike I would lose more and more "gravity" until it eventually stopped and even the smallest bump would see me floating free in space again

 

[joinerjohn]

then lets asume that I have a bike with me and pedal in the oposite direction just as fast as the station spins, effectively cancelling my rotational velocity.

as I rode faster on the bike I would lose more and more "gravity" until it eventually stopped and even the smallest bump would see me floating free in space again

Very interesting Col, I've never thought of that !!!!! Very nice if it could be done...
God I'll not sleep tonight now for thinking about that. Grrrrrrrrrrrrrrrr


PS, I bet I dream of 2001 a Space Odyssey tonight now. Cheers.

 

[ColJack]

it was an episode of Babylon 5 that set me off..
the one where Sheridan is "falling" from the central train thing to the outer wall..
they say he's going to die when he hits the "floor" but he's not really "falling" is he, he's just floating to the outer wall, he's not accelerating due to gravity and whatever speed he was moving when he left the train is the speed he'll be doing when he hits the "floor"..

it's more likely that something that's attached to the "floor" will hit him like a freitght train.. inertia and all that..