Glencoe Physics Chapter 9 Momentum and Its Conservation

Glencoe Physics Chapter 9

• Momentum and Its Conservation

Air Bags

• How exactly does an airbag prevent serious injury in an auto accident?

Baseball

• Why are baseball players encouraged to “follow through” when hitting the ball with a bat?

Why does a cannon move backward when firing?

Highway safety

• What can we do to make highways safer for people?

Common usage of the term “Momentum”

• A team that has momentum is on the move and is going to take some effort to stop.

• “Going into the final weeks, the St. Louis Cardinals have the momentum."
• The headlines declare “Pittsburgh Steelers Gaining Momentum."

• A team that has a lot of momentum is really on the move and is going to be hard to stop.

Momentum (from latin, meaning movement)

• Momentum is a physics term; it refers to the quantity of motion that an object has.

• Refers to how hard something is to stop.

Momentum Defined

• So momentum of an object depends on the amount of stuff moving (mass), and the velocity at which the stuff is moving.

• Question? Under what conditions of motion would a semi-truck and a roller skate have the same momentum?

Equivalent Momenta

Momentum Facts

• Momentum is a vector quantity

• Velocity and momentum vectors point in the same direction

• SI unit is the kg·m/s ( no special name)

• Momentum is a conserved quantity

• Momentum is directly proportional to mass and velocity of object

Momentum Facts

• A net force is needed to change a particular object’s momentum (a change in velocity)

• Something big and slow can have the same momentum of something small and fast

Momentum Examples

Sample problems

• Find the magnitude of the momentum of a car of mass 725 kg moving at a velocity of 100. km/h.

Sample problems

• Calculate the velocity of a car that has a mass of 2175 kg and the same momentum as the previous car.

Impulse

• In order to change the momentum of an object, a force must be applied

• Gives an alternative statement of Newton’s second law…..
• Watch as a little mathematical magic is performed!