What is Momentum?

The faster a body is moving the more kinetic energy it has. It also has momentum.
When working out what happens to bodies as a result of explosions or collisions it is more useful to think in terms of momentum than in terms of energy.

• you should be able to use the conservation of momentum (in one dimension) to calculate the mass, velocity or momentum of a body involved in a collision or explosion and ...
• to use the ideas of momentum to explain safety features.

Momentum, mass and velocity are related by the equation:

momentum = mass × velocity
               (kg m/s)                            (kg)                       (m/s)

Momentum has both magnitude and direction.
When a force acts on a body that is moving, or able to move, a change in momentum occurs.
Momentum is conserved in any collision/explosion provided no external forces act on the colliding/exploding bodies.

When a collision happens the total amount of momentum must be the same before and after.

HT      Force, change in momentum and time taken for the change are related by the equation:

force   =   change in momentum / time taken for the change
   (N)                                                    (kgm/s)                                                                               (s)

This means that the faster the momentum of an object changes, the bigger the force making it change.

Imagine a car hits a brick wall. If we can increase the time it takes for the driver to lose his / her momentum then the smaller the force slowing him / her down so the more likely they are not to get injured.

momentum change is fast  =  big force           momentum change is slow  =  smaller force

All the safety features below are designed to increase the time it takes for the momentum change to happen.

air bags	crumple zones	child seats	seat belts