Every object that is moving has momentum. The more mass an object has, and the faster it moves, the more momentum it has. Momentum is defined by the equation:
momentum = mass × velocity, or p = m v
Momentum, p, is measured in kilograms metre per second (kg m/s). Mass, m, is in kilograms (kg) and velocity, v, is in metres per second (m/s). An object at rest has a velocity of zero, so its momentum is zero. Velocity has a direction, so momentum is a vector quantity that points in the same direction as the velocity. If the velocity stays the same, doubling the mass doubles the momentum.
Worked examples: a trolley of mass 4 kg moving at 3 m/s has momentum 4 × 3 = 12 kg m/s. A car of mass 1200 kg travelling at 15 m/s has momentum 1200 × 15 = 18 000 kg m/s. A cyclist and bike of total mass 80 kg moving at 5 m/s have momentum 80 × 5 = 400 kg m/s. Rearranged, v = p ÷ m, so velocity = momentum ÷ mass.