A farmer tosses a rope over a beam at the top of a barn. He ties one end of the rope to a bale of hay. He then raises the bale up to the barn loft by pulling down on the loose end of the rope. Why does the input force have to be greater than the force needed to lift the bale?
Input forces need to be greater than the actual force needed to lift the bale, because of Friction. Some input energy is lost due to friction, because no simple machine, in this case a pulley is perfect.
