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Philip Wood
Jul30-11, 01:52 PM
PF Gold
P: 953
For example, if you lower the object gently by hand, you are exerting an upward force on the object (so the net force on the object is zero, and it doesn't gain speed), so the object exerts an equal and opposite force, i.e. a downward force, on your hand. This force does work on you, specifically on your arm muscles, as you lower your hand. Your muscles acquire internal energy and become a small amount hotter.