How does pulley make work easier?

Answer 1

A simple example is to imagine you're sitting on a swing attached to a rope and the rope goes up over a pully attached to the ceiling and back down. You could pull down on the other end of the rope to pull yourself up. It turns out the force you pull down with is only half of your weight, and it is actually pretty easy!

My first year physics prof did this demo and pulled himself up 30ft to the ceiling in a large classroom. Why is it easy? If you look at the forces on the pully in isolation, the force pulling up on it must be equal to your weight (call this force W). There are two downward forces from the two ends of the rope hanging down which must balance the upward force. When you're not accelerating the forces on the ends of the rope are equal. Let the rope forces equal R. You get the following equaltion:

W = 2R

R = W/2