2. Glencoe Physics Chapter 9
Momentum and Its Conservation

3. Air Bags
How exactly does an airbag prevent serious injury in an auto accident?

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

5. Why does a cannon move backward when firing?

6. Highway safety
What can we do to make highways safer for people?

7. 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.

8. 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.
1330 Jean Buridan “the true measure of an object’s motion”
1600’s Rene Descartes “quantity of motion
Galileo “Momento”
Newton “Momentum”

9. Which is probably harder to stop????? Why?

12. Yep…….that’s p for Momentum!!!
Momentum Defined
Yep…….that’s p for Momentum!!!
p = m v
p = momentum
m = mass
v = velocity
Unit must be kg m/s

16. Road Train in the Australian Outback
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?
Road Train in the Australian Outback

17. Equivalent Momenta
Car: m = 1800 kg; v = 80 m /s p = 1.44 ·105 kg · m /s
Bus: m = 9000 kg; v = 16 m /s p = 1.44 ·105 kg · m /s
Train: m = 3.6 ·104 kg; v = 4 m /s p = 1.44 ·105 kg · m /s

18. 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

19. 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

20. Momentum Examples p = 45 kg · m /s at 26º N of E 30 kg · m /s 3 m /s
9 km /s
26º
Now, find the vertical and horizontal components of the momentum>>>>>

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

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

23. 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!
Magic???

29. When an impulse (force applied over a period of time) is applied, a change in momentum will occur

30. “Big Bertha” 400-ton barrel

31. Shells weighed 7 tons!!!