Conservation of Momentum

Understanding Conservation of Momentum

  • The law of conservation of momentum states that the total momentum of an isolated system remains constant if no external forces act upon it.
  • Momentum is a vector quantity, meaning it has both magnitude (size) and direction.

Calculating Momentum

  • The momentum (p) of an object can be calculated using the formula: p = mv, where ‘m’ is mass and ‘v’ is velocity.
  • The SI unit for momentum is kilogram metres per second (kg m/s).

Collision and Explosion

  • In a collision, the total momentum before the collision is equal to the total momentum after the collision. This demonstrates the principle of conservation of momentum.
  • Similarly, in an explosion, the total momentum before the explosion (usually zero) is equal to the total momentum after the explosion.

Effect of Mass and Velocity on Momentum

  • From the momentum formula, we can deduce that objects with a bigger mass or velocity will have a larger momentum.
  • Therefore, if an object is moving quickly or is very large, it will be harder to stop. This means it has a lot of momentum.

Applications of Conservation of Momentum

  • The principle of conservation of momentum is used in many real-world situations, such as traffic accident analysis, predicting the motion of objects in space or in calculating how objects will move in computer games.

Impulse and Change in Momentum

  • The impulse of a force is the change in momentum that it causes. It is equal to the force multiplied by the time over which the force acts (Impulse = Force x time).
  • The greater the impulse on an object, the greater the object’s change in momentum. Therefore, to produce a large change in momentum, a small force could be applied over a long period of time, or a large force could be applied briefly.

Stopping Distance

  • The stopping distance of a vehicle (or any moving object) also relates to momentum. The heavier the vehicle or the faster it is going, the longer the stopping distance, because a lot of momentum needs to be lost to bring the vehicle to rest.
  • Items such as airbags in cars are designed to increase the amount of time it takes for a person to stop moving in a collision, therefore reducing the force experienced by the person.