When there is a car crash, the car, its contents and the passengers decelerate rapidly. They experience great forces because of the change in momentum, which can cause injuries. Modern cars have safety features that absorb kinetic energy in collisions. These typically include:
These features reduce injuries to the people in the car by absorbing energy from the impact. These features absorb energy when they change shape. This reduces injuries to the people in the car. They increase the time taken for the change in momentum on the occupants' bodies, and so reduce the forces involved and any subsequent injuries.
Seat belts stop you tumbling around inside the car if there is a collision. However, they are designed to stretch a bit in a collision. This increases the time taken for the body's momentum to reach zero, and so reduces the forces on it.
Airbags increase the time taken for the head's momentum to reach zero, and so reduce the forces on it. They also act as a soft cushion and prevent cuts.
Crumple zones are areas of a vehicle that are designed to crush in a controlled way in a collision. They increase the time taken to change the momentum of the driver and passengers in a crash, which reduces the force involved.