IS白痴問題(about force)

1)的確，在物理上回答有關重量問題時以newton作為單位回答才是正確的，以kg表達的是質量；但重量、質量只在物理上有明顯界定，拋開物理，只要別人看得懂就行了。

2)正如上面提及，kg是質量單位而n是力的單位，兩者不能互換，你只能說一kg的質量在某星球上感受到的重力為何。
由於F=mg，重力=質量x地心加速度
而地心加速度在地球上約為10ms-²，在月球上則約為1.6ms-²
因此1kg質量在地球上感受到的重力為10N
1kg質量在月球上感受到的重力為1.6N

3)兩件物體間的摩擦力會除著加在他們身上的力增加或減少而作出調整，務求抵消所有力，此時摩擦力是變數；但當加在物件身上的力大於最大摩擦力時（物件在運動時），摩擦力便會是常數。因此摩擦力是常數與否，完全取決於物件的運動情況。

4)在一些情況下，作用力和反作用力互相抵消，例如質量加給地球的重力和地板加給質量的反作用力
在另一些情況下，作用力和反作用力不能互相抵消，例如火箭引擎噴出氣體能使火箭加速前進。

1. 平時磅重is measure your mass, therefore the unit is kg. but measuring the weight, the unit is newton.

2. weight is equal to mass times gravity. therefore on earth, 1kg is equal to 10N

3. In physics, a contact force is a force between two objects (or an object and a surface) that are in contact with each other. This is distinct from a non-contact force (a force that acts over a distance), such as gravity or magnetic attraction/repulsion.

A contact force has two components. The part of the force that lies within the plane of contact is friction, which must be overcome for the two objects to slide relative to one another along that plane. The part of the force that is perpendicular to the plane of contact is called the normal force. Friction is proportional to the normal contact force, and the constant of proportionality is denoted by μ.

4. action and reaction pair are equal but opposite in direction. and most important of all, they are acting on different objects. therefore you can't cancel each other out.

hope i can help you...