How do pulleys work to provide a mechanical advantage?

1 Answer
Oct 6, 2015

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

Explanation:

I always found this diagram very useful!
Ramalho, Nicolau, Toledo, Os Fundamentos da FísicaRamalho, Nicolau, Toledo, Os Fundamentos da Física
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!!!