Momentum

Momentum is defined as

Ft = m(v₁ - v₀)

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

Ft = m(v₁ - v₀)

The units for the right side of the equation are kilogram.meter/second (or kg.m/s)

Ft = m(v₁ - v₀)

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.

In order to change the ball's momentum to zero, a certain amount of impulse is necessary.  If the time during which the ball is stopped is longer, the force will be less.