Forces in Physics

What are Forces in Physics?

A force describes, quantitatively, the interaction between two objects. A force is a vector quantity: its has a magnitude and a direction. You need to exert a force to pull a box on the floor. You use force to push a table. The weight of an object is the force of attraction that the earth exerts on this object. This interaction may be at a distance or through contact. Forces are used to push or pull stationary objects, to stop moving objects, to change direction of moving objects.
Forces always exist in pairs: a force of action and a force of reaction (third law of Newton). Action and reaction forces acts on different objects and have equal magnitudes.
A force is represented mathematically by a vector because both magnitude and direction are important to describe the force.
The SI unit of a force is the Newton. 1 Newton = 1 Kg × 1 m/s2
Therefore, the newton (N) is the magnitude of the force applied to an object of a mass of 1 Kg in order to acquire an acceleration of 1 m/s2.

Classification of Forces

A force can be put in one of the two classes: Forces with contact and forces at a distance.

A) Examples of forces with contact

1) The force exerted by person to push a trolley
2) The force (tension) exerted by a string on a suspended object
3) The force exerted by the ground on a table in a room (normal force)

B) Examples of Forces at a distance (also called field forces)

1) The force exerted by a planet (Earth for example) on any object with a mass.
2) The force exerted by an magnet on another magnet.
3) The electric force exerted by an electric charge on another electric charge.

Types of forces acting on objects