Forces & Newton's Laws

This lesson covers forces and Newton's laws of motion, which form the core of A-Level Mechanics. Newton's laws explain why objects move the way they do and provide the mathematical framework for analysing the effect of forces on motion.

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Types of Forces

Force	Description	Direction
Weight ($W = mg$W=mg)	Gravitational force on an object	Vertically downwards
Normal reaction ($R$R or $N$N)	Contact force perpendicular to a surface	Perpendicular to surface
Tension ($T$T)	Force in a taut string, rope, or cable	Along the string, away from the object
Friction ($F$F)	Force opposing motion or tendency to move	Opposite to direction of motion (or tendency)
Thrust/driving force	Applied force propelling an object	In the direction of motion
Resistance/drag	Forces opposing motion (air resistance, etc.)	Opposite to direction of motion

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Newton's Three Laws

First Law (Equilibrium)

An object remains at rest or continues to move at constant velocity unless acted upon by a resultant (net) force.