GCSE Physics: Forces and Motion Guide

Speed and velocity

Speed = distance ÷ time. Velocity is speed in a given direction. On a distance-time graph, the gradient represents speed; a steeper line means faster movement, and a flat line means the object is stationary.

Acceleration

Acceleration = change in velocity ÷ time taken, measured in m/s². On a velocity-time graph, the gradient represents acceleration, and the area under the graph represents distance travelled.

Newton's laws of motion

Newton's first law: an object stays at rest or at constant velocity unless a resultant force acts on it. Newton's second law: force = mass × acceleration (F = ma). Newton's third law: every action has an equal and opposite reaction.

Momentum

Momentum = mass × velocity. In a closed system, total momentum is conserved before and after a collision or explosion.

Common mistakes

• Confusing speed (a scalar) with velocity (a vector, which includes direction).
• Misreading gradients on distance-time versus velocity-time graphs.
• Forgetting F = ma requires a resultant (overall) force, not just any single force acting.