Artificial Gravity by rotation

[DoctorDanny]

I have a question for the more brainy people on this forum.

How exactly does rotating an object (say a station or a part of a spacecraft) generate gravity?

I understand that a person standing on a moving surface will move with the same speed as that surface. Same as standing in a train I guess.
With the lack of gravity pulling you 'down' wouldn't you just float off if you'd jump?

I get the general idea but I feel like I'm missing part of the logic here.

Explain away!

 

[FrogsFriend]

http://www.bogan.ca/physics/coriolis.html

Enjoy.

 

[Ian Doncaster]

How exactly does rotating an object (say a station or a part of a spacecraft) generate gravity?

I understand that a person standing on a moving surface will move with the same speed as that surface. Same as standing in a train I guess.
With the lack of gravity pulling you 'down' wouldn't you just float off if you'd jump?

The thing to remember is that it's not gravity: it's a simulation of it. You won't just float off, but you won't land in the same place you'd expect from real gravity either. So long as you stick to slow movements, mostly aligned parallel to the axis of rotation, you won't notice much difference. Big or fast movements will behave very oddly, though (especially in large open spaces where the atmosphere itself is affected)

Jumping won't work, but if you were in a rotating cylinder, with no atmosphere to drag you down, and you used some means of flight to enter the cylinder without ever touching the sides, you could hover above the surface then.

 

[Gelbrock]

Imagine you are a stone in Davids sling.... and he is swinging it around above his head. The stone is forced into the cup of the sling. Creating gravity.

Its as simple as that.... in theory.

The faster the sling (space station) spins the harder you are pushed against the cup of the sling (the edge of the space station).

The trick is to spin it just the right speed to match our gravity on earth. Too hard and we will be squashed into the wall. To slow a spin will mean we will be lighter and walking normally will be not as simple. But would be great for moving cargo as mentioned in the newsletter as everything would be lighter.



It works the opposite way to which gravity works on earth which is why it can be confusing. Here we all walk around on the outside of a ball (the Earth shape) as gravity pulls us to the centre of the planet.

In a spinning space station as shown in the new newsletter we are forced away from the centre so we would walk on the inside of the ball (space station). This is rather handy as if we walked on the outside of the space station.... we would of course die a horrible death

As far as standing on a moving surface as you mentioned. If the space station was enclosed and you could not see the stars outside Im not sure if you would even get the feeling of the floor moving even though it is spinning around as it would (should) be a very smooth movement.

Hope that answers the question.

 

[Slawkenbergius]

With the lack of gravity pulling you 'down' wouldn't you just float off if you'd jump?

You basically get thrown in a more-or-less straight line back at the floor of the space-station. Because you were travelling at the same rate as the floor, you'll land in almost the same place even, though I believe you do drift a little. So if you tried to jump straight upwards, you'd probably fall a little distance away from where you started.

Juggling will probably be a much more impressive feat on a rotating space-station, so maybe they'll earn extra money in the future. I'm not sure about what would happen with trapeze acts...

 

[natte hond]

if you swing your arm around , you feel the blood rushing to your hand.
that's the same principle.
now lay a rock in your hand and do the same thing.
if you maintain the continuous speed you can open your hand without losing the stone.
as long as you keep your hand under the stone.
like how your clothes stick to de walls in your washing machine when it is at speed.
I think this is the most simple explanation one can give.

now for some thing more complex.
this principle was also used to accelerate voyager 1 and two.
by letting them fall just around planets.
the gravity of the planets pulled them towards them, but for them having to much speed and the right angle they escaped the gravity field faster then they arrived.
this is the sling shot principle.
it works as good on a planet as of one.
its the same as a cricket player does when throwing a ball
only he cannot throw fast enough to leave orbit

 

[Gelbrock]

Slaw and Ian touched on a good point.

In the spinning space station scenario if you jump straight up you will not land in the same spot (very close too) as I see it.

The bigger the space station the less this will apply I think.

Great if you want to try to break the long jump record.... as long as you jump the right direction of course.

....or.... will the curvature in the floor negate the impact of the spinning effect.... see, now Im boring myself..... goodnight....

 

[Gimi]

There are some complications to this, namely the coriolis effect. When water drains out of the tub it rotates, weather systems on earth rotate, all this is down to the coriolis effect. Earth is a sphere, which means that when it rotates an object on the equator moves slightly faster than an object north or south of the equator. This causes rotation in free flowing liquid or gases. (this is a rather simplified explanation, I'm writing this on my pad)
When smaller objects rotate the relative speed difference increases. So on a rotating space station your feet will be moving slightly faster than your head and this causes dizziness and nausea. The way to avoid this is to reduce the relative speed difference and you do that by making the rotating space station bigger. I don't remember how big a space station has to be to make it "comfortable", but its fairly big. I suspect that the rotating ring on the imperial cruiser is a tad small. It looks good though, and I'm sure Frontier have considered this when building the Elite universe.

 

[Susimetsa]

I'm sure most of us have played with a bucket of water in our childhoods - holding it in your hand and swinging it in big circle. Do it fast enough and the water will stay in the bucket even when the bucket is upside down above your head.

If you missed this when you were a kid, I'd recommend you run to your bathroom now.

 

[roryscarlett]

We need to understand some basic physics here. What is gravity? It is the attraction of two particles with mass. Due to the attraction, the two particles experience an acceleration towards each other. So from a human's point of view we experience an acceleration towards the (much larger) planet Earth! The FORCE of gravity a particle experiences is this acceleration multiplied by the particle's mass.

Rotating objects are completely different. All objects (at rest) will not experience any acceleration unless a FORCE is exerted on that particle (one of Newton's basic laws). That means that if a particle is moving at constant velocity (no acceleration) and no FORCES are acting upon it, it will go in a straight line!

Now imagine a stone on the end of a length of string. Swing the stone. The stone moves in a circle, why? According to Newton if no FORCES are acting on the stone, it must travel in a straight line, therefore the string FORCES the stone to travel in a circle, that FORCE is centripetal force. Centrifugal force does NOT exist, it is merely the stone's inertia wanting to travel in a straight line while the centripetal FORCE accelerates the stone into a circular path, THAT IS WHAT YOU WOULD EXPERIENCE IN A ROTATING SPACE STATION. Alter the speed of rotation and the acceleration differs, alter the distance from the center, the acceleration differs.

Understanding that we experience gravity through acceleration will help you understand how this idea of pseudo artificial 'gravity' works. It should be called rotational acceleration to stop confusion but artificial gravity makes it instantly understandable if not totally accurate!

Hope this helps!

 

[DoctorDanny]

Great awnsers guys. Who knew you could learn so much new stuff talking about computer games Thanks!

 

[roryscarlett]

I think that's part of the reason why Elite has become so popular, it's far greater than the sum of its parts!

 

[Frank]

Centrifugal force does NOT exist, it is merely the stone's inertia wanting to travel in a straight line while the centripetal FORCE accelerates the stone into a circular path,

Why complicate matters by saying that inertial forces aren't real?

http://xkcd.com/123/

 

[roryscarlett]

I love it, that's hilarious!

 

[roryscarlett]

Though I am intrigued about the fact that if you jump, what happens then? Technically you will only experience 'gravity' when you are in contact with the station as it's the station itself that's providing the centripetal force! If you lose contact with the station will you become 'weightless' again and float off? If you jump you are only in contact with the atmosphere. This atmosphere is nowhere near viscous enough to provide any real FORCES? Would be interesting to get some points of view on this!

 

[FrogsFriend]

If the station is split into compartments I'd guess at a 'moon-walk' style bounce with the added coriolis sideways movement.
But in one big open cylinder I'm not sure.

... heads for Google.

EDIT: the truth is out there:
http://www.dvandom.com/coriolis/spacestation.html
With lots of nice diagrams.

 

[AtomicHorror]

Though I am intrigued about the fact that if you jump, what happens then? Technically you will only experience 'gravity' when you are in contact with the station as it's the station itself that's providing the centripetal force! If you lose contact with the station will you become 'weightless' again and float off? If you jump you are only in contact with the atmosphere.

Yes, but you're still more or less horizontally stationary relative to the floor and your body still has angular momentum (it's trying to leave the centrifuge through the floor), so will always fall back down (atmosphere or none) and unless it's a really big jump, or a very small station, you should land back down pretty much where you expect to.

Jumping won't work, but if you were in a rotating cylinder, with no atmosphere to drag you down, and you used some means of flight to enter the cylinder without ever touching the sides, you could hover above the surface then.

This occurred to me before and I wonder how the developers intend to deal with this when docking. We have to enter the docking cylinder and then land on the surface, which is going to be rotating relative to us. We can match our rotation to that of the docking doors, because we're sitting on the axis of rotation. But as soon as we try to "lower" ourselves towards the cylinder floor, we'll find that the floor is moving under us, possibly quite fast.

Electromagnets might help a ship interact with the centrifuge enough to dock safely.

 

[Ian Doncaster]

This atmosphere is nowhere near viscous enough to provide any real FORCES?

FrogsFriend's diagrams seem to generally assume no atmosphere, and have you "landing" again because your sideways velocity is more than sufficient anyway.

However: the atmosphere - assuming something close to Earth pressurisation - is definitely viscous enough to do that. In the absence of external forces, the air resistance from the atmosphere will bring you to a stop fairly quickly (consider how much more difficult it is to walk stably in a 30mph wind)

I would imagine the stations would generally be quite compartmentalised, or the larger ones could get some interesting internal wind systems from shear in the atmosphere. Smaller compartments would get air pressure gradients across them, but probably not significantly enough to be uncomfortable.

 

[Ian Doncaster]

This occurred to me before and I wonder how the developers intend to deal with this when docking. We have to enter the docking cylinder and then land on the surface, which is going to be rotating relative to us. We can match our rotation to that of the docking doors, because we're sitting on the axis of rotation. But as soon as we try to "lower" ourselves towards the cylinder floor, we'll find that the floor is moving under us, possibly quite fast.

A few options - it's something I'm interested to see how they manage it, too.

The smoothest way under powered flight might be to fly in along the centre of the cylinder until you were "above" the pad, then turn to fly a widening spiral around the cylinder, slowing increasing your angular speed and radius so that when you touched down on the pad your relative velocity with respect to it was near-zero. Getting the thrust right to do that would be very tricky, though - autopilot only, or very practised manual pilots. It'd make the original Elite's docking look very easy indeed.

Safer would be to have the docking pads on their own rings, which could be spun up or down independently of the main station body: spin down for takeoff and landing, then once you're safely docked and locked, spin back up for microgravity to resynchronise with the station rotation. Or perhaps have clamps on the axis of rotation that you can fly into and be locked, just needing the relatively easy task of matching rotation, then dragged on rails down to the docking pad.

Alternatively again, if the station is large, and the docking corridor relatively small compared with the station, the linear velocity of the docking pad isn't going to be very big anyway, so some decent landing gear will be able to absorb the velocity you get as you land, so long as you don't land sideways to the rotation.

 

[Susimetsa]

Interesting bit, this one: "running anti-spinward [. . .] At just the right speed, the robot comes to a complete halt with respect to space outside the station, and no longer has any force pushing him up towards the axis. So he floats for a bit until the wind reduces his speed."

Basically, the station needs to be big enough to provide artificial gravity that is pleasant (no big difference in the amount of gravity between your head and your feet or you will feel sick). The bigger it is, the slower it should rotate to retain about 1g gravity for the outer rim. And the slower it rotates, the more danger there is that by walking or running anti-spinward, you will find yourself becoming weightless and toppling over every now and then...

Wait, there's a fault in my logic... Need to think of it a bit more...