I recently watched 2001 and 2010 recently. It seems as if (WAG) that the satellite that Dr. Floyd visits on his way to the moon was like a centrifuge that would fling the inhabitants to the outermost walls of the station, simulating gravity. The Discovery seems to be the same idea, just on a smaller scale. Ditto for the Russian ship in 2010 that has a giant spinning centrifuge in the center of it. I am having a hard time imagining how this could work in zero G. It seems to me that in zero G, you would remain weightless no matter how fast that thing would spin, because gravity would still be required to fling you to the outermost walls of the station. However, since it was written by Arthur C. Clarke, I think there must be something to it, and I just don’t understand it. There is also a part in 2010 that is confusing. John Lithgow and a Russian character latch onto the Discovery while it is spinning end over end. They latch onto the middle first, since it has less spin, and then proceed to one of the ends of the ship. As they progess to the end, Lithgow complains of growing heavier. I assume this is because of the spin of the ship pushing harder against them as they progress farther down the ship. But since they are progessing down the ship slowly, aren’t they also assuming the speed of the spin of the ship themselves? Again it seems as if gravity would have to be in play somehow, but it can’t since they are in zero G. Help! Someone 'splain it to me!
Any mass wants to continue its motion in a straight line and will do so unless affected by an external force.
So, your spinning ring is trying to fling you in a straight line off into space. If the floors magically disappeared that is what would happen. Luckily (at least in this case), we can’t move through solid objects so your straight line off into space is stopped by the floor. The force trying to throw you off the spaceship feels like gravity sticking you to the floor.
It’s the same thing at work as that Barrel Roll (or whatever it’s called) amusement park ride that sticks you to the walls. Imagine hanging on to the outside of the barrel as it spins to get an idea of what forces are acting on you here. If you let go you’re going to go flying off.
The gracity is being simulated by the acceleration felt at the rim of these rotating parts. That is acceleration in the Physics sense, not the vernacular sense of increasing speed. Have you ever seen the amusement park ride with the rotating cylinder? The riders are spun in a twenty foot, or so, diameter cylinder at a sufficient rate as to allow the friction against the side walls to keep them pinned as the floor drops out from underneath them.
Another way to simulate gravity in space would be to accelerate (in a speed sense) the ship at one G. A tough fuel problem, no doubt, but the crew would feel as though the rear of the ship was “down” and they were in normal Earth gravity.
It’s acceleration that “feels like” a force when your in that accelerating frame of reference.
And because Dr. Brantley would retroactively give me a failing grade in physics, I’ll add that (according to him, anyway) there is no such thing as “centrifugal force.” It’s just Newton’s good old First Law of Motion.
Not only does it “feel like” a force it is indistinguishable from gravity. This was one of Einstein’s interesting leaps of logic that got Relativity all together in his head. If I sealed you in a spaceship with no windows undergoing 1g of acceleration there is no test you could perform on the spaceship that would identify the fact that the force is being caused by rocket motors speeding you up instead of just sitting on the surface of the earth under 1g of gravity.
Ahhh…the phantom force. Centripetal force is the thing at work on our spaceship. The centripetal force is the force pulling any object in a circular path. Centrifugal force seems to exist but doesn’t. The best explanation I heard for this one is to picture a ball sitting on the seat in a car. If you turn to the left the ball, from the occupant’s perspective, seems to have a force acting on it pushing it to the right. However, a person outside the car watching all of this can see that the ball is obeying Newton’s laws of motion and travelling in a straight line…it is the car that is moving underneath the ball. The occupants of the car call the ‘force’ pushing the ball to the right centrifugal force but as just shown it doesn’t really exist.
Also, realize that centripetal force is not really a ‘force’ either (such as gravity) but rather describes the behavior of a force. A satellite orbiting the earth experiences centripetal force but it is actually gravity that is providing the actual force.
This link has a pretty nifty (if simple) animation that shows what we are all talking about here.
Your are the red dot. The white arrow shows the direction you would travel if the green line snapped (that’ll make sense if you click on the link). Now imagine a floor at the tip of the white arrow moving around with it. The white arrow will continuously push you into the floor thus simulating gravity.
Hope that helps.
However, if I sealed you in a space station with no windows and spun it so as to supply 1 g of acceleration at the outer wall, you could determine that the force was being caused by rotation and not linear acceleration. The surface of a bucket of water placed on the floor will have a measurable curve under rotation, but not under linear acceleration.
I don’t mean to be picky here Whack-a-Mole, but there’s no accelerated frame of reference that will make that water appear flat.
???
Those two paragraphs seem to be at odds with each other. I agree that on the rotating spacestation we could discern a difference but on our spaceship accelerating under 1g you can’t (assuming you somehow don’t know you’re on a spaceship).
On the rotating ring we have two forces working on you. One force is the spinning that is trying to throw you in a straight line from the spacestation. The floor, however, is pushing back on you and changing your direction of travel constantly.
In our spaceship accelerating in a straight line everything is going in the same direction. Your bucket of water won’t help you here to decide what is really happening.
MAXWELL,
You are correct about something. If you are not on the outer rim and moving with it, you will not feel the effect of the centripital forces.
You are in-correct about gravity being needed to fling you to the outer wall.
Here’s an interesting example from the movie: Please note I’ve never seen 2010 but remember a scene from 2001 where a runner is running laps on the inner wall of the outer rim of the space ship. The “gravity” he feels is dependant on which way he runs. If he runs in same direction as the spin, he will grow “heavier” as his movement adds to his rotational velocity.
BUT, if he runs opposite to the spin, and runs fast enough (fast enough to cancel spinning of space ship), he will become weightless and will no longer be affected by the spinning of the craft.
Before the rest of you jump in here, I have ignored the fact that the air in the space ship is spinning and will bring the floating runner back to the edge, where he will be bouncing off chairs and keyboards until he is moving with the space ship again.
But Maxwell does bring up the very good point that you must first get off the axis of spin and attach yourself to the craft before the spinning works as it is supposed to. In the movie they do this climbing down ladders I think.
Not so! If you were in a constantly accelerating spaceship, accelerating at 1 g, that might be true (although there would be no angular gradient as on a planetary surface – that’s always bothered me), but in a rotating coordinate system you will not only have the fictitious centrifugal force, but you will also have the unusual Coriolis force as well. This will occasionally give you weird effects.
Another odd feature – since the Centrifugal force varies with distance from the center, your head will feel a different “gravity” than your toes. I believe the gradient is independent of the size of the cylinder.
This is true of gravity as well. Your feet feel gravity more strongly than your head (although I don’t know if the mathematical relationships between spinning in this case and gravity are equivalent). I’ll grant you this effect is very small here on earth but it’s there. If you were standing on a star that was collapsing into a black hole (nevermind how you’re surviving standing on a star in the first place) the difference in gravity between your feet and your head would stratch you out like a piece of spaghetti (for a ‘small’ black hole at least…you might be ok as far as becoming spaghetti goes on a ‘big’ one).
Also, read up a bit and you might notice that I already agreed that a spinning system would be distinguishable from a linear acceleration.
So doesn’t this contradict your earlier statement? If I’m in a sealed spaceship that’s sitting on the ground, I can measure that the force on my feet is greater than the force on my head. If I’m in a sealed spaceship that’s accelerating at 1g, I can measure that the force is the same on both. Hence, the two situations are distinguishable. What’d I miss?
We’ll need Chronos or other equally well-versed physics person in here to describe this better.
What I can say is this. Perhaps one of the most fundamental aspects of Special Relativity is that the laws of physics are the same in all inertial frames. Basically this says that no kind of observation at all, even measuring the speed of light, will help you determine if you are at rest or moving (indeed, there is no such thing as at rest).
I may be missing something so hopefully someone will be along to clear this up.
Einstein’s Weak Equivalency principle only applies to point particles. Any extended object will experience tidal forces.
Yes but keep in mind you’re talking SR not GR.
In GR, Einstein’s Strong Equivalency principle says the laws of physics in an inertial system in which there is a uniform gravitational field are the same as in a uniformly accelerated system in which there is no gravitational field. However in a strong gravitational field (Black Holes, Neutron Stars) this is no longer true.
Actually what I said is not what I meant to say. GR says that the laws of physic are the same in all refernce frames not just inertial frames.
Although it is uncertain (at least to me) whether the conservation of energy holds in GR.
Okay, we’ve got two really good challenges here, and I’m going to try to answer both the same way. (Actually, Ring may have beat me to it by using the phrase “point particles”, but I’m going to expand on it for the benefit of those who missed this critical point.)
Point #1: In regards to gravity, my left side and right side are being pulled in slightly different directions, and that will distinguish it from the accelerating spaceship where all is being pulled in the same direction.
Point #2: In regards to gravity, my bottom is being pulled down harder than my top is, and that will distinguish it from the accelerating spaceship where all is being pulled at the same strength.
Solution: Remember when you were a kid, and someone told you that nothing can be in two places at once? And you went over to the border between two places, straddled the border, and announced, “Look! I am both here and there at the same time!” Then you got older, and realized that what they really meant was that a point particle cannot be in both places at once.
That’s what’s happening here. For a specific point, it is impossible to tell whether the push is the result of gravity or of acceleration. But if you analyze the effects on two different points in the same system, then you will be able to tell the difference.
Okay, now someone who actually knows something about physics will please correct me. 