Force may be defined as an external agency (a push or a pull) which changes or tends to change the state of rest or of uniform motion or the direction of motion of a body.
The dimensions of force is [MLT⁻²] and SI unit is Newton (N).
A force applied on an object can produce four types of effects such as
(I) Force can start or stop a motion.
(II) Force can change speed of an object.
(III) Force can change the direction of motion of an object.
(IV) Force can change the shape of an object.
Aristotle’s Fallacy and Galileo Galilei
The Greek philosopher, Aristotle give the view that if a body is moving, some external force is required to keep it moving.
Example: When an arrow shot from a bow keeps flying since the air behind the arrow keeps pushing it.
However, Aristotle’s views were proved wrong by Galileo Galilei (1564-1642) about two thousand years later on. It was observed that external forces were necessary to counter the opposing forces of friction to keep bodies in uniform motion. If there were no fiction, no external force would be needed to maintain the state of uniform motion of a body.