Forces and motion

Force

A push or pull that can change the motion of an object. Measured in newtons (N).

Mass

The amount of matter in an object. Remains constant everywhere. Unit: kilogram (kg).

Weight

The force of gravity acting on a mass. Weight = mass × g (g ≈ 10 N/kg on Earth). Unit: newton (N). Changes with location.

Newton’s First Law

An object remains at rest or continues moving at constant speed in a straight line unless a resultant force acts on it.

Newton’s Second Law

F = m × a. The force on an object equals its mass multiplied by its acceleration. 1 N accelerates 1 kg at 1 m/s².

Newton’s Third Law

For every force there is an equal and opposite force (the two forces act on different objects).

Speed

How fast an object is moving. Average speed = total distance ÷ total time. Units: m/s or km/h.

Acceleration

Rate of change of speed. a = change in speed ÷ time. Unit: m/s².

Deceleration

Slowing down. The resultant force acts in the opposite direction to the motion.

Resultant force

The single force that has the same effect as all the forces acting on an object combined.

Distance-time graph – horizontal

Object is stationary (speed = 0).

Distance-time graph – straight slope

Constant speed. Steeper slope = higher speed. Slope value = speed.

Distance-time graph – curve

Changing speed (accelerating or decelerating).

Speed-time graph – slope

The slope equals the acceleration.

Ticker timer

Device that makes dots on paper tape at regular time intervals (often 50 per second). Wider spacing = higher speed.

Contact force

Force that requires objects to touch (e.g. friction, tension, normal force, air resistance).

Non-contact force

Force that acts at a distance (e.g. gravity, magnetic force, electrostatic force).

Energy

The ability to do work or cause change. Unit: joule (J).

Law of Conservation of Energy

Energy cannot be created or destroyed; it can only be transferred or changed from one form to another.

Work

Energy transferred when a force moves an object in the direction of the force. W = F × d. Unit: joule (J).

Power

Rate of doing work or transferring energy. P = W/t or E/t. Unit: watt (W = J/s).

Gravitational potential energy

Energy stored due to an object’s height above the ground.

Kinetic energy

Energy of a moving object.