Ten-pin bowling balls are available with different mass. A fast moving ball with low mass can be as effective as a slow ball with high mass. This is because it is the momentum of the ball that is important in the collision with the pins, and momentum depends on mass and velocity.
When a force acts on an object that is moving, or able to move, it causes a change in momentum in the same direction as the force (because the velocity changes). The longer time that the force acts, the bigger the change in momentum.
- reducing the acceleration (force = mass × acceleration) which means reducing the velocity of the body more slowly.
- reducing the momentum of the body more slowly.
- Crumple zones The car occupants are in a strong safety cage. The front and back of the car are designed to crumple in a collision, increasing the distance and time over which the occupants are brought to a stop.
- Airbags The body hits the airbag, which is compressed, increasing the distance the body moves and the time it takes to stop.
- Seatbelts These are designed to stretch slightly so that the body moves forward and comes to a stop more slowly than it would if it hit the windscreen or front seats. After a collision, the seatbelts should be replaced because having stretched once, they may not work properly again.
- Cycle and motorcycle helmets These contain a layer of material which will compress on impact so that the skull is brought to a stop more slowly. They should be replaced after a collision as the material will be damaged andmay not give good protection again.