9.2 Momentum and the Impulse-Momentum Theorem

What does a force acting on an object do?

It deliverse an impulse that changes it's momentum.

The seatbelts in your car are made of webbing that is designed to have a significant stretch when supporting large forces. Why is this useful?

REASON Suppose a car crashes into a fixed barrier and comes to rest. The driver will come to rest as well. Increasing the time over which the driver comes to rest will decrease the force on the driver. If the seatbelt can stretch, the driver can still be moving after the car has stopped—the driver can come to rest over a longer time. Increasing the time reduces the force, and thus the chance for injury. ASSESS This makes sense. If the seatbelt could not stretch at all, a driver or passenger would stop much more suddenly, which would increase the force and the likelihood of injury.

What is the magnitude of an object's momentum?

The magnitude of an object's momentum is simply the product of the object's mass and speed, or p=mv. A heavy, fast-moving object will have a great deal of momentum, while a light, slow-moving object will have very little. Two objects with very different masses can have similar values of momentum if their speeds are very different as well.

Impulse-Momentum Theorem

states that the impulse on an object equals the object's final momentum minus the object's initial momentum

total momentum

sum of all momentum