Momentum and Impulse

Have you ever wondered… How a tae kwon do expert can break a stack of cement blocks? Why falling on a cement floor hurts more than falling on the grass? Why a follow through is important in golf, baseball or boxing? These all relate back to Newton’s First Law of Motion – Inertia!

Momentum We know that it is more difficult to stop a large truck than it is a small car when they are both moving at the same speed. We say that the truck has more momentum than the car. Momentum is inertia in motion or mass in motion. More specifically Momentum = mass x velocity p = mv

Momentum is a vector quantity. Velocity = 10km/hr Momentum? 10km/hr p = mv p = (5,000kg)(10km/hr) p = 50,000 kgkm/hr Mass = 5,000 kg 10km/hr p = mv p = (1,000kg)(10km/hr) p = 10,000 kgkm/hr Mass = 1,000 kg

Momentum A moving object can have a large momentum if it has a large mass, a high speed or both. Why does the truck have more momentum than the car, if they are both moving at the same speed? The truck has more mass! When would a small car have more momentum than a large truck? If the car was moving considerably faster than the truck When would the roller skate and the truck picture below have the same momentum?

Changes in Momentum If the momentum of an object changes, what thing(s) influence this change? Changes in mass, velocity or both! Often the mass of an object will stay unchanged, which means that velocity of the object must change. This results in an acceleration. From our last unit, what produces this acceleration? A Force!

Impulse The greater the force acting on an object, the greater its change in velocity and the greater its change in momentum Impulse is the change in an object’s momentum. Impulse = force x time I = Ft The greater the impulse exerted on something, the greater the change in momentum for that object I = ∆(mv)

Decreasing and Increasing momentum To increase the momentum of an object, it makes sense to apply a force for as long as possible Why do baseball players follow through when they hit baseballs? To apply the force of the hit for as long as possible, increasing the momentum of the baseball Decreasing Momentum If you were driving to school and your car went out of control would you rather hit a cement wall or a haystack, why?