Gravity
 

Rolling down a slope

Gravity makes it more difficult to force things to move uphill and easier to force them downhill. Children will find that carrying, sliding and rolling are easier downhill. A slope is a simple machine that diverts part of the force sideways. The extent to which the slope diverts gravity sideways depends on its angle, so that objects take longer to roll down a shallower slope.

Children can compare sliding a brick using a rubber band along a level surface, measuring the extent to which the rubber band is stretched. Tilt the surface and force the load to slide uphill. Measurements of the extent to which the rubber band is stretched are taken. Observe and compare the measurements of the force required to slide the load downhill.