Laws of Motion - SS1 Physics Past Questions and Answers - page 3

Friction is a force that opposes the motion of an object when it is in contact with a surface. Newton's laws of motion can be applied to understand the behaviour of friction. According to Newton's first law of motion, an object at rest tends to stay at rest unless acted upon by an external force. In the case of friction, when an object is at rest on a surface, the static friction force prevents the object from moving until a force is applied to overcome it.

The normal force is a contact force exerted by a surface on an object that is in contact with it. Newton's third law of motion states that for every action, there is an equal and opposite reaction. In the case of the normal force, when an object exerts a downward force due to its weight, the surface exerts an equal and opposite upward force as the normal force. This reaction force prevents the object from sinking to the surface.