Cool ... and an excellent example of a simple but powerful experiment. I've never thought about centrifugal acceleration that way. (Hint: Think of a jet of water in place of the chain. The source of energy driving the motion is different, but the trajectories are similar.)
[This message has been edited by Marvin McInnis (edited 05-01-2014).]
Think of a jet of water in place of the chain. The source of energy driving the motion is different, but the trajectories are similar.
Ah yes, the trajectory. Reminds me of the last time I drank beer while out in the woods.
Marvin, here's a question for you. Since the pot pushes the end of each rod on the chain up as the rod pivots (which supplies that extra bit of acceleration), what would the end result be if the experiment was done in a high speed elevator? For argument's sake, let's say a hundred foot chain would only drop 20 feet before it hits the "floor" in either scenario (to eliminate the variable of a greater weight of chain due to an increased drop). Would the trajectory of the chain be higher, or lower, as it's being pulled out of an ascending pot compared to a stationary pot... or to a descending pot?
[This message has been edited by Patrick (edited 05-01-2014).]
Since the pot pushes the end of each rod on the chain up ...
No. The desending chain, which is inelastic, pulls itself out of the reservoir. The key consideration is that the speed is the same everywhere along the chain. Say the chain is descending at 50 feet per second. That means that the chain must also be moving upward at 50 fps as it leaves the reservoir.
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Would the trajectory of the chain be higher, or lower, as it's being pulled out of an ascending pot compared to a stationary pot... or to a descending pot?
I think it would be the same, as long as the elevator is moving at constant velocity (i.e. not accelerating or decelerating).
[This message has been edited by Marvin McInnis (edited 05-01-2014).]
No. The desending chain, which is inelastic, pulls itself out of the reservoir. The key consideration is that the speed is the same everywhere along the chain. Say the chain is descending at 50 feet per second. That means that the chain must also be moving upward at 50 fps as it leaves the reservoir.
Marvin, did you watch the second video that Boonie linked to? They spent a considerable amount of time discussing how the pot also "pushes" the chain, and this is why I was wondering if movement (up or down) of the pot itself might affect the trajectory of the chain.
I disagree. At the very least, they failed to consider the stiffness/flexibility of the links connecting the masses. I think that is probably important, as well as the mass distribution. I would like to see the experiment repeated with moderately stiff rope or wire cable, either of which has a continuous mass distribution and would eliminate the alleged dynamic "kick" from the reservoir. Of course, both rope and cable have significant internal friction, which might serve to dampen the dynamic effects.
[This message has been edited by Marvin McInnis (edited 05-01-2014).]
Marvin, did you watch the second video that Boonie linked to? They spent a considerable amount of time discussing how the pot also "pushes" the chain, and this is why I was wondering if movement (up or down) of the pot itself might affect the trajectory of the chain.
The pot does not really push up on the chain (unless you are talking about opposing forces ect..) but it does store the potential energy of the chain’s kinetic energy. Much like a syphon works, as long as your output is lower than your input, gravity will do the rest. The chain has a surface tension cause by the links. The faster the chain drops, the less time the chain has to “flex” and therefore pulls itself up from the pot. The limits will be reached when the chain reaches its terminal velocity.
Interesting experiment would be to make a loop… A motor that would provide just enough force to bring the chain back up in the pot and make an endless loop.
I suppose you could test that theory by lifting and/or lowering the pot while the chain is playing out, and see how it affects the trajectory. Actually, since the experimenters are holding the pot in their hands during the experiment, the pot must be pushing down on their hand anyway (equal and opposite force to the one pushing the chain up). Maybe ask them if they feel an extra downward push when the chain starts playing out.
[This message has been edited by Blacktree (edited 05-01-2014).]
Maybe ask them if they feel an extra downward push when the chain starts playing out.
A better experimental design would be to put the reservoir on a sensitive scale, sitting on a firm table. If the reservoir is indeed "pushing" the chain, the weight of the reservoir should decrease smoothly as the chain is depleted, but there should be an abrupt drop in measured force as the last link of chain breaks contact with the bottom of the reservoir.
Saw this on Mythbusters last month. Jamie did the same thing with a really large beaded-chain. The metal beads were each the size of large marbles...it was impressive, and obviously worked the same at the little chains in all the other videos.
I disagree. At the very least, they failed to consider the stiffness/flexibility of the links connecting the masses. I think that is probably important, as well as the mass distribution. I would like to see the experiment repeated with moderately stiff rope or wire cable, either of which has a continuous mass distribution and would eliminate the alleged dynamic "kick" from the reservoir. Of course, both rope and cable have significant internal friction, which might serve to dampen the dynamic effects.
I saw the wire rope that holds the hook and swivel come loose from the deadman clamp once. 1 5/8" diameter IIRC. Even after the hook hit the drilling floor, the cable just kept coming off the main spool, up thru the crown block sheaves and it arced up pretty high above the first sheave (big pulley). (That was looking back over my shoulder as I was running down the steps--I think I only touched about 3 of the 30 steps )
I suppose you could test that theory by lifting and/or lowering the pot while the chain is playing out, and see how it affects the trajectory. Actually, since the experimenters are holding the pot in their hands during the experiment, the pot must be pushing down on their hand anyway (equal and opposite force to the one pushing the chain up). Maybe ask them if they feel an extra downward push when the chain starts playing out.
All they'll feel is the pot getting lighter as the chain feeds out. There is no upward force on the pot/chain other than the hand holding it in place. If the post is held stationary, that force is equal and opposite to gravity and is constant. As the chain feeds out, the mass reduces and less force is required to hold the pot.
As far as holding the pot is concerned, it's no different than pouring water out of a pitcher.
