Forces and motion
A force is a push or pull. Contact forces include friction and tension; non-contact forces include gravity, electrostatic and magnetism. Weight W = mg. Resultant force decides whether an object accelerates: F = ma.
Speed is scalar; velocity is vector. Acceleration a = Δv/t. Distance-time graphs: gradient is speed. Velocity-time graphs: gradient is acceleration and area is distance.
Newton’s laws
- 1: If resultant force is zero, the object stays at rest or at constant velocity.
- 2: F = ma.
- 3: Forces between two objects are equal and opposite.
Stopping distance = thinking distance + braking distance. Thinking distance increases with speed, tiredness, alcohol and drugs. Braking distance increases with speed, poor brakes, ice and more mass. Work done W = Fs. Momentum p = mv and is conserved in a closed system.
Download Forces slides (PowerPoint)
Taught with support from Joseph Danso, Science Lecturer in London. Book a session.