Momentum

Ft = m(v₁ - v₀)

1. Left term Ft is called (1)
2. Right term m(v₁ - v₀) is called (2)

Your body experiences a change in momentum, for while you are moving you have some momentum, but after the collision you have (1) .  Since impulse is equal to the change in momentum, the force exerted on your body to stop it depends on the time during which that force acts.  If you are not wearing seat belts and have no airbag, your head may continue forward until it is stopped quickly by the windshield.  The equation tells us that if the time (t) is small, the force (F) will be (2) .  Seat belts and airbags increase the time a person decelerates, reducing the force exerted on the person.