Masses & Springs - Mass, Springs, Force. Forces in 1 Dimension - Force, Motion, Friction. Gravity Force Lab - Gravity, Force, Mass. KS2 Bitesize Science - Forces in action : Play. KS2 Bitesize Science - Forces in action : Play. KS2 Bitesize Science - Friction : Play. Friction is a force between two surfaces that are sliding, or trying to slide, across each other. For example, when you try to push a book along the floor, friction makes this difficult. Friction always works in the direction opposite to the direction in which the object is moving, or trying to move. Friction always slows a moving object down. The amount of friction depends on the materials from which the two surfaces are made. Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tyres skidding on the road. Sometimes we want to reduce friction.