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Pascals Principles.

  1. Jan 10, 2005 #1
    Ok it's about fluids.

    You have a tube 100% full of water, no air at all.

    Corked both ends.

    Hit the one cork with a hammer, the amount of force that it hit with is = to the force that hit the other cork. and knocks it out.

    Now I was once doing collissions and I was trying to find a situation which has 100% efficiency. I eventually failed to figure out one. As no vacuum could ever be perfect in practice.

    So I asked my teacher if there could possibly be a 100% efficient thing. He said there is nothing at all which is 100%. Then did the speech about car engine is only 40% efficient. and alot of other things.

    Now I find that this Cork water situation isn't 100% efficient as per other situations. My teacher said something along the lines that it is = to the other force. Seemingly 100% efficient cause of the "=to"

    Which is right? I can understand that its very very close and the air resistance would make the total amount not 100%, but transmission from cork to cork cant be 100% is it?
  2. jcsd
  3. Jan 10, 2005 #2
    people usually use "efficient" describe energy, are you talking about the energy from the hammer can 100% transfer to the other cork? or the force? or both?
    make it clearer pls
  4. Jan 10, 2005 #3
    imagine a photon hitting an electron, isn't that a 100% elastic collision?
  5. Jan 10, 2005 #4
    well the force which is exterted from the first cork, because of the hammer, through the water/liquid and into the other cork. Is it 100% the same energy and force from which the first cork was hit with?

    as for photon on electron, there can be charge transfer, and the medium(vacuum) isn't perfect so other particles may influence on the collission.

    Of coarse in theory such things can be 100%, but practically.
  6. Jan 10, 2005 #5
    I was saying a photo collide with an electron is elactic, I am not saying the electron/photo colliding with other particle after or b4 the collision. That is ANOTHER COLLISION and that collision is also elastic.....
    When your teacher said no collision is elastic, yes, he is right (in our daily life). collision will cause heat, sound.. etc. which loss energy. But what is heat, sound ..etc? It is the motion of particles. If two elemtary particles collide, would it cause heat, sound...etc? NO. ALL COLLISION OF ELEMTARY PARTICLES ARE ELASTIC (assuming no fission, fussion, excitation of electron... etc.) The energy can go nowhere in such collision except go back to the particles itself. (don't say energy radiates away, photon is also a particles)
    OKAY back to your original question, NO in both case. as you say, friction between water and tude, friction between water molecules, the deformation of the first cork when you hit it, the pressure applied on water makes it compress....etc. everything cost energy. you can't just transfer all energy to the second cork. How about the force? the friction between the cork and tube will transfer some force to the tube, and to your hands.... applied your newtons law, action force = reaction force. the force acted on the second cork will be LESS than the original one... not 100% either, unless you make an assumtion there has no friction and the water cant be compressed (which is unrealistic), no 100% efficiency in your case...
  7. Jan 10, 2005 #6


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    Plus the water will get just a bit hotter from the increase in pressure.
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