Force & Friction 摩擦力一問

Actually, their answers are 50% correct.

When you first start to move a bench, you need to exert a force to overcome the (limiting) static friction given by the ground. Once the bench has started moving, you only need to exert a force to balance the kinetic friction of the ground.
Since kinetic friction is generally smaller than static friction, this is the reason why the force keeping the bench moving is less than that required to start it moving from rest.

舉例啦，如果我有 1N friction 啦。

咁我開始既時候比既力唔可以係 1 N咁少架 bor，
因為1 N - 1 N= 0N，咁就無net force啦，
咁佢就唔會由at rest變到陏。

所以呢，一開始要比大過 1 N既力，
例如 2N，
咁就有1N net force。

咁佢陏緊啦嘛，咁我如果只需要keep佢constant speed，
就咁比 1N佢就可以against到 friction啦。

所以一開始要 >1N
之後係要 ≧1N

2009-03-05 20:50:12 補充：
Why do u say so??