Types of Forces

Force definition

A push or pull that can change motion or shape

Vector quantity

Has magnitude and direction

Weight

Force due to gravity acting on mass

Weight direction

Always acts downward towards Earth’s centre

Weight unit

Newtons (N)

Mass vs weight

Mass is amount of matter; weight is gravitational force

Reaction force

Upward force from a surface supporting an object

Reaction force direction

Perpendicular to the surface

Friction

Force opposing motion between two surfaces

Friction direction

Opposite to direction of motion

Air resistance

Frictional force acting against objects moving through air

Air resistance increases with

Speed and surface area

Tension

Force in a stretched rope, cable or string

Tension direction

Along the rope, away from the object

Thrust

Forward force from engines or pushing

Upthrust

Upward force on objects in fluids

Upthrust cause

Difference in pressure in fluids

Magnetic force

Force between magnets or magnetic materials

Electrostatic force

Force between charged objects

Resultant force

Single force that has same effect as all forces combined

Balanced forces

Resultant force = 0 → no change in motion

Unbalanced forces

Resultant force ≠ 0 → acceleration occurs

Key idea

Forces can change speed, direction or shape depending on how they act