Question

How do pulleys work to provide a mechanical advantage?

Answer 1

In a very simplistic way the pulley "splits" forces "reducing" them!

Explanation:

I always found this diagram very useful!

As you can see a person needing to lift `120N` ends up applying only `15N`.

The weight of `120N`, when applied to the pulley, is split into two components by the presence of the rope and pulley. This process can go on and on to reduce even further the amount of force needed (last picture)!

Obviously you must "pay" for this...in terms of height! If it is true that `15N` can lift a box weighting `120N` it is also true that the box will only lift of few centimetres!

At the end of the day you'll need to continuously apply `15N` to lift the box up to the desired height. The Energy used in the process of lifting the box at a certain height will be the same with the pulleys or without them!!!