A pulley is a very simple mechanism that makes it easy to move or lift a load. This BBC clip explains how they work and shows a group of children moving a 12 tonne truck.
Gears consist of rotatting wheels which have teeth or cogs that fit into the teeth of another wheel. This can cause a change in speed or direction of the forces that are applied.
To raise the mass 1 metre using one wheel you need to pull the loose end of the rope a distance of 1 metre with a force equivalent to 10kg or 100N (newtons).
To raise the mass 1 metre using two wheels you need to pull the loose end of the rope a distance of 2 metres with a force equivalent to 5kg or 50N (newtons).
To raise the mass 1 metre using four wheels you need to pull the loose end of the rope a distance of 4 metres with a force equivalent to 2.5kg or 25N (newtons).
