Conservation of momentum

How it is used

Used for collisions, explosions, the recoil of guns and rocket propulsion. Students write 'total momentum before = total momentum after' and must keep track of directions with plus and minus signs. It holds even when kinetic energy is not conserved.

Example sentences

1. Using conservation of momentum, find the speed of the two trolleys after they stick together.

2. The recoil of the cannon is explained by conservation of momentum.

Common collocations

• law of conservation of momentum
• total momentum
• momentum before and after
• isolated system

Related terms

• momentumThe product of an object's mass and its velocity (p = mv). It is a vector and is measured in kilogram metres per second (kg·m/s).
• elastic collisionA collision in which the total kinetic energy of the objects is the same before and after the impact. Momentum is conserved in every collision, but kinetic energy only in elastic ones.
• impulseThe effect of a force acting over a time interval, equal to force multiplied by time. It equals the change in an object's momentum and is measured in newton seconds (N·s).
• conservation of energyThe principle that energy cannot be created or destroyed, only transferred between objects or converted from one form to another. The total energy of an isolated system stays constant.
• Newton's laws of motionThree basic laws that describe how forces affect motion: an object keeps its state of motion unless a net force acts, net force equals mass times acceleration, and every action has an equal and opposite reaction.

More terms: Energy, Work and Momentum

• energy
• work
• power
• kinetic energy
• potential energy
• efficiency