四滑輪

四滑輪
圖例：
FZ = 施加在繩自由端的力
FL = 物體重力
s = 繩自由端的位移
h = 物體的位移
這個例子用來說明如何利用合適的滑輪來省力。使用滑輪可以省力但是要花費更多的距離。在每幅圖中，所做的功都是相同的。
Description
FZ × s = FL × h 
10 cm × 100 N = 10 J
20 cm × 50 N = 10 J
30 cm × 33 1/3 N = 10 J
40 cm × 25 N = 10 J
FZ = Rope tension or effort force
FL = Load or resistance force
s = Rope displacement (distance pulled) or effort distance
h = Height (distance load is raised) or resistance distance
An illustration showing how pulleys are used to obtain a mechanical advantage. Using additional pulleys decreases the force required but increases the distance required to raise a load the same amount. In each instance here the mechanical work done is the same, work being the product of force and distance.
FZ × s = FL × h 
10 cm × 100 N = 10 J
20 cm × 50 N = 10 J
30 cm × 33 1/3 N = 10 J
40 cm × 25 N = 10 J
通過這個亦可證明功的原理。