friction F.2

船向前比力
水面會比番相對應ge friction向後
所以會reduce左個speed
lee個好易理解

而第二個例子所講ge concept就對 F.2黎講太深
主要係因為friction係分
static friction 同 kinetic friction

大概講一講
static friction係會隨住你比ge力
佢會作出相同 ge reaction force
但係static friction會有max
所以唔會一路至無限

而當過左 max static friction
就會變成 kinetic friction

船係用 kinetic friction黎行
而車係用 static friction黎行 (大多數有輪ge都係static friction)
如果車輪ge (static) friction太細
你就會好易比大過 static friction ge 力
咁就會變左 kinetic friction
而車以kinetic friction黎行駛就係所謂 ge 「跣軚」

<------------------------------------------------------------------------------->

如果唔明上面d 野 ge話
你就只要知道
1). 兩個例子中 ge friction係唔同ge
2). 船果個就係：推一個野會慢慢停果種friction
3). 而車果個friction唔夠大，越開得快就越易跣軚

Firstly, the grooves on tyres does not help to speed the car up. They are used to display water when the car is driving on a wet road. Otherwise the water will form a thin layer between the tyres and the road and the car will slip. In fact the grooves reduce the friction between tyres and road. That's why in Formula 1 car racing, 光頭 tyres are used in good weather condition so as to increase friction. Friction is needed in driving the car because the car is not sliding on the road. It required friction to transform the rotatary motion of the wheel to forward motion of the car. If the friction is not good enough (like in the case when a car is trapped in wet mud), the car cannot move efficiently.