物理問題 力學的問題

由於推力小於摩擦力，所以不動，消耗在摩擦力上，只將摩擦力減少了，例：　F 為摩擦力　ｆ為推力

ｆ-F=ma 由於ｆ小於F, 所以a為負值

當你向右推，所以人會向左動．意思是你推的方向　相反了．

例如：　你大力向牆推一下，你身體會向後．

就是f-F=ma

首先，力不能被消耗，能量才能被消耗。

在这个案例中，力使物件与地面互相摩擦，从而引致物件对摩擦做功。（假设物件在地上）

那么，人的能量去哪呢？答案是自己。那人在做运动。
人付出的能量转化为其内能。

2008-10-18 22:57:14 補充：
情景：人推静止物件。
当人的推力为5时，物件的摩擦力最大为5，不可能为10。
因为摩擦力不可能大于推力。
在静摩擦中，摩擦力会随着施力的上升而上升（不会大于施力），直至被克服。

若物件与地面的最大摩擦力为10，而两人各用5单位的力推动它，
则三力刚好抵消，物体还在原处。
除非两人的合力大于10，否则物件不会被移离原处。

In physics, there is no work done as the object has not been moved at all.

But in terms of energy, you need to increase your body metabolism in order to exert a force. The energy is provided by the chemical reaction within your body and is dissipated as heat, so that you would feel your heart beats faster and also you would sweat.

Some supplement.

I would say the force you applied is less than the MAX. STATIC FRICTION, when you applying a force on the object, the force you applied is the same in magnitude with the friction but in opposite direction, as a result net force is zero.

If you want to move the object, the applied force must be larger than the MAX. STATIC FRICTION. The friction is changing as you are applying different force.