When a force acts on an object that is moving, or able to move, a change in momentum occurs. The equations F = m × a and a = (v − u)/t combine to give the equation F = m ∆v/∆t where m∆v = change in momentum, ie force equals the rate of change of momentum. • Students should be able to explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds with reference to the concept of rate of change of momentum. • Students should be able to apply equations relating force, mass, velocity and acceleration to explain how the changes involved are inter-related.