Free Fall Scenario: 100kg Piston Kinetic Energy After 20m Drop

[NoTime]

Dear No Time,
When an object descends in a cylinder filled with water, which is directly linked at top and bottom by an identical cyliner which is also filled with water, describe the chain of events that must take place for 1chunk of water measuring 1 cubic foot to move 1 linear hand!

Sorry, this isn't an answer to anything I asked you.

 

[beckerman]

Lets remember who asked the original question

 

[beckerman]

Lets also observe who seems to have had very little to say in opposition to my most recent posts.

 

[rcgldr]

You keep mentioning the piston is accelerating, but seem to imply that once the water starts moving, the water isn't accelerating. However, in order for the piston to acceleration, the water also has to accelerate, and the acceleration is limited by the mass of both the piston and the water.

In addition to momentum of the water resisting acceleration, as the water speeds up, viscosity of the water resists the flow, slowing the rate of acceleration, until the system reaches a terminal velocity.

 

[beckerman]

I have acknowledged that the piston and the water have to accelerate in unison, and also that there would be a terminal velocity that would be slower that the terminal velocity would be in air. I have also acknowledged that the 1kg of weight circulating the water through the system would do it slowly at first. What I am objecting is the theory that the object would descend exactly as it would in a pool. I made a comparison earlier to a balanced see saw. Dave commented that my reasoning was not accurate because I was ignoring inertia. He was right to an extent but I do not feel he discredited my reasoning. His comment was that you would have to use a balanced see saw with weight at either end equal to the weight of the water in each cylinder as a model. If you had a balance beam with 1000kg at either end and added 1kg to one side that one side would go down, and if there were nothing to stop its travel it would continue to accelerate.

 

[rcgldr]

What I am objecting is the theory that the object would descend exactly as it would in a pool.

You're correct here, it's not the same. In a pool, fluidic drag is resisting the movement of the weight. In the weight in a closed filled tube case, the momentum and viscosity of the water are resisting the movement of the weight. In a vertical, open tube, both the water and the weight are near free fall with only aerodynamic drag against the water and weight resisting the movement.

 

[DaveC426913]

What I am objecting is the theory that the object would descend exactly as it would in a pool.

As the one initially propsed the comparison to sinking in a pool, let me say that I did not mean to suggest that it would happen just as in a pool. I was merely saying that it would be no faster than that.

I concede though that it's a lousy comparison. In a pool, the weight is always fighting stationary water. In your tube however, the water picks up momentum and the weight is essentially carried along.

Why don't you sketch and upload a rough diagram? I'd like to ensure we're talking about the same things. Example, I keep going back to a circular donut, rather than an elongated 'paperclip' shape, but both introduce other problems.

 

[beckerman]

Ok, I can do that if you direct me how. The "paper clip" shape you described is the shape I was invisioning. I am a little confused about your comment. You stated that in stationary water the piston would "always" be fighting stationary water. Conversely in the tube scenario it does not fight the water during the whole length of its travel. Saying the descent would be just as slow as the descent in a pool seems contradictary to these observations.