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# Physics > Forces Overview

A force can be explained as being an influence that makes an object accelerate. It may be experienced as a push, pull or lift. The main forces discussed in school physics are gravitational force and frictional forces.

Forces in school physics are usually measured with a force meter, usually called a Newtonmeter. The unit of force is the Newton (symbol N)

Gravitational force

All objects of mass have gravity and as such, attract other objects towards them. The bigger the mass, the bigger the gravitational forces involved. Every physical object has gravity, even you but because your mass is so small, the force is weak. Massive objects such as planets have massive gravities and can attract other planets, comets and other celestial bodies over long distances.

Frictional force

When an object moves over another, the friction between the two surfaces converts kinetic energy into heat. Friction is not a fundamental force as it is made up of the electromagnetic forces between atoms in the surfaces.

Frictional forces act in the opposite direction to that of the movement of the object. Friction can be both useful (in walking) and detrimental (slipping on ice)

Balanced forces

Forces always work in pairs with one force working in the complete opposite direction to the other. In diagrams, forces are commonly shown as arrows with the bigger arrows showing the larger of the two forces.

For example, imagine a conker on the end of a piece of string. The weight of the conker pulls the conker down due to gravity but the string also pulls the conker up. The two forces here are equal but work in opposite directions.

A boat floating on water uses the same principle. The weight of the boat is balanced by the upthrust of the water and as such the two opposing forces are equal.

Unbalanced forces

When a car drives down a road, the horizontal forces acting upon it are unbalanced. The engine provides a bigger force forwards than the backwards forces of air resistance and so therefore it moves forwards. If the forces in this case were equal, the car would be stationary.