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Thread: Simpleton's Query

  1. #1 Simpleton's Query 
    Time Lord zinjanthropos's Avatar
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    Physics is not my thing but a couple of us were wondering about this the other day: When a ball is thrown directly up into the air does it take more energy to launch it than for gravity to bring it back down to earth? or is it the same? I was thinking it would be the same but I don't know why. Please help


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    Forum Isotope Bunbury's Avatar
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    The energy of the ball is the same, but it does take more nergy to launch it because of the inefficiencies of the throwing arm, the utlization of food to create the energy and so on.


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    Forum Senior TheObserver's Avatar
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    Well total energy is conserved, but a lot of energy is lost thermally due to drag. You need to be a bit more specific on what you mean by more energy up than down. Do you mean to ask whether more work is done by friction on the way up as the way down? Just considering gravity alone and ignoring the friction as well as the energy expended chemically by your body, the work done by gravity to move the ball up is the same as it is to move it back down since gravity is conservative, except opposite in sign so that the total work done is zero.
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    Time Lord zinjanthropos's Avatar
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    Quote Originally Posted by Bunbury View Post
    The energy of the ball is the same, but it does take more nergy to launch it because of the inefficiencies of the throwing arm, the utlization of food to create the energy and so on.
    I never thought of that.

    Does Earth's gravity exert the same pull at all stages of the ball's ascent or descent? Disregarding friction, should I be able to under the same circumstances, throw a ball higher from where I stand, at the top of Mt Everest?
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    Quote Originally Posted by zinjanthropos View Post

    Does Earth's gravity exert the same pull at all stages of the ball's ascent or descent? Disregarding friction, should I be able to under the same circumstances, throw a ball higher from where I stand, at the top of Mt Everest?
    The earth's gravity decreases with distance from the earth's center. However, over the short distance you are able to throw something, it is practically constant. You could theoretically throw it higher from Mt Everest, but the difference would be insignificant.
    Gravity of Earth - Wikipedia, the free encyclopedia
    Gravity decreases with altitude, since greater altitude means greater distance from the Earth's centre. All other things being equal, an increase in altitude from sea level to the top of Mount Everest (8,850 metres) causes a weight decrease of about 0.28%.
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