CHAPTER 9 Momentum

Momentum is a vector quantity defined as the product of an objects mass and velocity Momentum describes an object’s motion Symbol for Momentum is p (lower case) Note: Uppercase P is Power Formula for Momentum is mass x velocity p = mv Units for momentum are kilogrammeters per second (kgm/s)

Momentum When we think of a massive object moving at a high velocity, we often say that the object has a large momentum. A less massive object with the same velocity has a smaller momentum. On the other hand, a small object moving with a very high velocity has a large momentum.

Momentum The faster you move, the more momentum you have and the more difficult it is to come to a stop. The more massive an object is, the more force it will exert on another object when they collide because of its momentum.

Impulse Impulse is defined as the product of force and the time over which an external force acts on an object. Symbol for Impulse is J Formula for impulse is Force x change in time J = F∆T Units of impulse are Ns or kgm/s

Impulse-Momentum Theorem The Impulse-Momentum Theorem states a change in momentum takes force and time. Change in Momentum (∆p) = Force x change in time (F∆T) ∆p = p f – p i therefore p f – p i = F∆T Since p = mv we can also say mv f – mv i = F∆T

ImpulseImpulse- Momentum Theorem Stopping time and distances depend on the impulse-momentum theorem. Highway safety engineers use the impulse- momentum theorem to determine stopping distances and safe following distances for cars and trucks. The impulse-momentum theorem is used to design safety equipment that reduces the forces exerted on a human body during collisions

On a trampoline, jumpers are protected from injury because the rubber reduces the force of the collision by allowing it to take place over a longer period of time.

Egg Impulse Demo

Worksheet 6.A

Conservation of Momentum In its most general form, the law of conservation of momentum can be stated as follows: The total momentum of all objects interacting with one another remains constant Regardless of the nature of the forces between the objects, Momentum is conserved in collisions

Conservation of Momentum When two or more objects collide, the total momentum of the two objects together remains the same. The total initial momentum = the total final momentum M 1 v 1i + m 2 v 2i = m 1 v 1f +m 2 v 2f If initially both objects are at rest, then the initial total momentum = 0

2 major types CollisionsCollisions Perfectly inelastic collisions 2 objects collide and then move together as one mass (coupled). Kinetic Energy is not constant Some of the energy is converted to sound and heat (like in a car wreck). Elastic collisions 2 objects collide and return to their original shapes with no change in total kinetic energy. After the collisions, the objects move off separately.