What do you think would happen on a solid concrete floor that could not flex to store energy from, and restore energy to, the can? I'm betting nothing would change, except that the balls already on the floor would not be bouncing around.
"What do you think would happen on a solid concrete floor that could not flex to store energy from, and restore energy to, the can?" ... the floor moves more than you think... like a bell that's been struck. However assuming that it did not flex at all, the Ping Pong Balls already on the floor would most likely stay in place. But because the floor does flex ... albeit slightly, then the nearby Ping Pong Balls are slightly kicked up in synchronization with the trash can.
Trashcans typically do not have flat bottoms. There are usually ridges molded into the bottom for rigidity. This would create an airspace under the can that is momentarily compressed when the bottle explodes creating an air spring underneath.
Here's another way to think of it. Imagine a tennis ball at the moment of maximum compression against the clay court. One side is flat, and there is energy stored in the rubber cover and compressed air inside. Now hold that thought; freeze the tennis ball in time. Okay, now change the tennis ball into a flexible plastic garbage can whose energy is stored in a pop bottle about to explode. It lies flat, "compressed" against the floor. Then, kaboom! Back to the tennis ball. The stored energy is released, it pushes back on the court, and bounces high. The trashcan does the same; the bottom bulges out, launching it into the air. The trashcan is just a flattened tennis ball frozen in time, awaiting the release of its potential energy.
So if we attach a sensor to one of the ping pong balls and tie that to a system on an elevator that instantaniously matches it upward velocity, will it ever escape the trash can?
C.W.
It's as though your question faded into another dimension and no-one except those tuned in to elevators,conveyors etc like ourselves saw it........I wonder why?
It's as though your question faded into another dimension and no-one except those tuned in to elevators,conveyors etc like ourselves saw it........I wonder why?
It's like when you're out with the horses...step in it once, it's an accident, step in it twice, ya ain't learned your lesson!
It's like when you're out with the horses...step in it once, it's an accident, step in it twice, ya ain't learned your lesson!
Where's the moderators when you need them? I'll have you know that ctwardell and myself have a very valid point to make, not to be taken so lightly! Humph!
Where's the moderators when you need them? I'll have you know that ctwardell and myself have a very valid point to make, not to be taken so lightly! Humph!
My appologies, I'd be happy to translate my comment to include any animal that is culturally acceptable to you all in the spirit of international brotherhood...or should it be peoplehood?? :0)
So if we attach a sensor to one of the ping pong balls and tie that to a system on an elevator that instantaniously matches it upward velocity, will it ever escape the trash can?
Only if the elevator is capable of unlimited acceleration. Remember the gas is pushing on the bottom of the trash can, so as the bottom moves up, the pressure of the gas increases. Which should act to push the contents out of the can, unless the elevator keeps accelerating.
What if you did the same experiment with the same can but this time the bottom was shaped like the bottom of a soda can? That way it couldn't expand out more in the middle of the bottom causing the upward motion of the rest of the can.
@PhiPi: More importantly, why did it jump a foot to the right? Where were the survivors buried? If I ask the OTHER man, which door would he choose? Recall that a pound of feathers indeed weighs more than a pound of gold, my learned opponent...
What do you think would happen on a solid concrete floor that could not flex to store energy from, and restore energy to, the can? I'm betting nothing would change, except that the balls already on the floor would not be bouncing around.
-Phil
I bet the can would hardly bounce on a concrete floor. (btw, you CAN flex a concrete floor, it's just lots harder) The whole can flexes from the pressure of the explosion so some bounce would happen on concrete, but not the giant leap seen on the springy wooden floor. (i.e. the initial bounce on a concrete floor would be more like the can's landing and second bounce on the video)
Instead of an explosion causing the downward acceleration of the can, drop it from a height of, say, five feet instead. Do you think the can will rebound?
If watch the trash can in the video as it lands from it's jump you'll see that it acts exactly like a dead-blow hammer.
@PhiPi: More importantly, why did it jump a foot to the right?
The can wasn't lined up with the floor supports, so it launched at a slight angle due to the non-uniform floor stiffness. If you've ever jumped on a trampoline, the same thing happens if you land off center.
It could have also moved to the right because a plastic bottle exploding doesn't give you an even amount of energy in all directions. The blast may have been focused more in one direction.
Looking at this frame, the trashcan is still on the ground and the explosion is going upwards, so presumably there is a reaction force going downwards like a rocket? Something happens after this - I'm not sure what. Compressed air under the can? A bounce from the wooden floor? Something else?
Also he tips water in first - presumably this is so the balls float on the water. The liquid nitrogen in the bottle probably is floating on the water too when it explodes. So there is a mass of water in the equation.
With reference to the video above, in this case the floor is the billiard ball and the trashcan is the ping pong ball
For the sake of argument, let's replace the billiard ball with a solid, immovable, incompressible wall. That way, the kinetic energy during the collision will be stored exclusively by the compression of the ping pong ball, and it will bounce back at the same speed with which it hit the wall. This is the same situation I alluded to in my post #35 above. Deflection of, and energy stored by, the floor is totally unnecessary to explain why the can jumps into the air. It all has to do with the energy stored within the can itself and its "de-deformation" upon release.
My original argument is that the Liquid Nitrogen and Ping Pong Ball demonstration was a variation of Newton's Cradle with respect to the trash can lifting off of the ground ... additionally the floor flexing slightly provides a possible explanation of the synchronized lift of the immediate surrounding ping pong balls at the same moment the trash can lifts from the ground.
Comments
What do you think would happen on a solid concrete floor that could not flex to store energy from, and restore energy to, the can? I'm betting nothing would change, except that the balls already on the floor would not be bouncing around.
-Phil
-Phil
It's like when you're out with the horses...step in it once, it's an accident, step in it twice, ya ain't learned your lesson!
My appologies, I'd be happy to translate my comment to include any animal that is culturally acceptable to you all in the spirit of international brotherhood...or should it be peoplehood?? :0)
Only if the elevator is capable of unlimited acceleration. Remember the gas is pushing on the bottom of the trash can, so as the bottom moves up, the pressure of the gas increases. Which should act to push the contents out of the can, unless the elevator keeps accelerating.
I bet the can would hardly bounce on a concrete floor. (btw, you CAN flex a concrete floor, it's just lots harder) The whole can flexes from the pressure of the explosion so some bounce would happen on concrete, but not the giant leap seen on the springy wooden floor. (i.e. the initial bounce on a concrete floor would be more like the can's landing and second bounce on the video)
If watch the trash can in the video as it lands from it's jump you'll see that it acts exactly like a dead-blow hammer.
Lawson
The can wasn't lined up with the floor supports, so it launched at a slight angle due to the non-uniform floor stiffness. If you've ever jumped on a trampoline, the same thing happens if you land off center.
Lawson
-Phil
Also he tips water in first - presumably this is so the balls float on the water. The liquid nitrogen in the bottle probably is floating on the water too when it explodes. So there is a mass of water in the equation.
With reference to the video above, in this case the floor is the billiard ball and the trashcan is the ping pong ball
-Phil
"I think this is the bit that Beau is referring to..." - and here as well :-)
http://www.youtube.com/watch?feature=player_detailpage&v=SUYnS7rj33w#t=1372s
My original argument is that the Liquid Nitrogen and Ping Pong Ball demonstration was a variation of Newton's Cradle with respect to the trash can lifting off of the ground ... additionally the floor flexing slightly provides a possible explanation of the synchronized lift of the immediate surrounding ping pong balls at the same moment the trash can lifts from the ground.