Forces

A force can be described as a push or a pull. There are the contact forces that arise when two objects make physical contact; and there are noncontact forces that are exerted without physical contact, such as gravity. Isaac Newton developed three laws relating force and mass. They are called the Newton's laws of motion. There are four main types of forces: normal force, frictional force, and tension force.

Gravitational force is the mutual attractive force between two uncharged masses. Normal force is the perpendicular component of the force of a surface pushing on an object. Frictional force is a component force between two surfaces that is parallel to the surfaces. It is divided into static frictional force (when the two surfaces do not move with respect to each other) and kinetic frictional force (when the two surfaces move, or slide over one another). Tension force is the force exerted by a rope.

Other forces include centripetal forces and restoring forces.

References and Further Readings

• Cutnell JD,Johnson KW. 2000. Physics. 5th Edition. (NY): John Wiley & Sons. 1064 p.