點解踏單車比走路快?

Q: 點解踏單車比走路快?速度可以差幾倍,但腳的移動速度分別不大

In the physics perspective, bicycle is, in fact, a kind of simple "machine". It has a low "velocity ratio". Hence, the distance moved by the bicycle (i.e. the load) is much longer than that moved by the legs of the cyclist (i.e. the effort).

Q: 而且踏單車好像沒有這麼辛苦, 點解?

There is relatively small frictional resistance between the rotating wheels and the road than between the feet and the road. Moreover, inertia and momentum do help to reduce the effort in cycling.

單車既行駛速度可以高達時速20至30公里, 但係人既走路速度都係每小時4公里左右, 速度當然差得遠.