Momentum is defined as the product of an object's mass and velocity. It is a vector quantity that depends on both the magnitude and direction of motion. During collisions or whenever a force acts upon an object, momentum changes occur. The impulse-momentum theorem states that the impulse on an object, which is the force applied over time, equals the change in momentum. Distributing the force of an impact over a longer period of time through compliant materials like sludge or crumpled car roofs can reduce the peak force and prevent serious injury. In interactions between objects, the total momentum is conserved according to the law of conservation of momentum.

2. What is Momentum?
Momentum may be defined by its equation:
Momentum is a quantity defined
as the product of the mass and
velocity of an object.

3. Unit of Momentum
• The equation illustrates that momentum
is directly proportional to an object’s
mass and the object’s velocity.

4. Momentum’s Proportionality

5. Momentum’s Proportionality

6. Momentum’s Proportionality

7. Momentum is a vector quantity
• Back to the Bowling Ball: To fully describe the
momentum of a 5 kg bowling ball, moving
westward at 2 m/s, you must include both the
magnitude and the direction of the bowling
ball’s momentum. (It would not be enough to
just say the ball has 10 kg.m/s momentum.)

8. Momentum: Sample Problem

9. Changing Momentum
• A change in momentum takes force
and time. To stop an object, it is
necessary to apply a force against its
motion for a given period of time.

10. Changing Momentum
In football, the defensive player
applies a force for a given amount
of time to stop the momentum of
the offensive player with the ball.

11. Changing Momentum
Serway/Faughn - Physics

12. • A force is applied to an object to change its
momentum.
• Impulse – the product of the force, and the time
over which the force is applied.
• Impulse – Momentum Theorem – the impulse
experienced by the object equals the change in
momentum
Changing Momentum
Serway/Faughn - Physics

13. Changing Momentum

14. Sample Problem: Force needed for change in
momentum (impulse)

15. Sample Problem: Force acting on a car while
braking.

16. Sample Problem: Force acting on a car
while braking.
(The car on the last slide.)

17. Increasing the time of an impact can reduce the
force of a collision.
Changing Momentum
This Inupiat (Alaska native people)
Family is playing a traditional game.
The blanket stretches and extends
the time of collision so that the
change in the girl’s momentum
occurs over a longer time interval.
A longer time interval requires a
smaller force to change the girls
momentum, than if she fell directly
to the ground (not a good idea.)
Serway/Faughn - Physics

18. Skydiver Lisa Boyer fell 3,810 meters
after her parachute failed to open.
She landed in a sludge pond and
survived ---unhurt!
If Boyer had landed on solid ground, she would have
come to a crashing halt in about 0.0001 sec.
The concentrated force of that abrupt landing would
have killed her instantly.

19. • But she landed in the sludge pond of a sewage
treatment plant. The soft, squishy sludge brought her
body to rest in about 0.03 sec ---30 times longer than
if she landed on sold ground.
• Because the force of the impact was distributed over
this longer time, it was never strong enough to cause
serious injury.
(Science World)
Falling into sewage sure
is gross, but it beats the
alternative.

20. Window washer Chris Saggers fell 22 stories to the roof a
car. He walked away with only a broken elbow. If he had hit
the roof feet first, the force would have been focused in a
small area, shattered his legs, and driven the bones into
his spine.
But Saggers landed sprawled out, with the force of impact
distributed evenly over his body. (Science World)
The car roof crumpled
so it lengthen the
time of the impact.

25. Conservation of Momentum
The total momentum of all objects
interacting with one another remains
constant regardless of the nature of the
forces between the objects.

26. Soccer Ball Collision & Conservation of
Momentum

27. Soccer Ball Collision & Conservation of
Momentum
Elastic Collision

30. • In every interaction between two
isolated objects, the change in
momentum of the first object is
equal and opposite to the change in
momentum of the second object.
Conservation of Momentum &
Collisions

31. Conservation of Momentum &
Collisions

32. Conservation of Momentum &
Collisions – Boater Problem

33. Conservation of Momentum &
Collisions – Boater Problem

34. Types of Collisions
• Perfectly inelastic collisions – When
two objects collide and move
together as one mass ---they stick
together after the collision. (like a
meteorite and the earth)

35. • Perfectly inelastic collisions
Types of Collisions

38. Elastic collision: two objects collide and
return to their original shapes with no
change in kinetic energy. Here again,
the total momentum remains constant.
Types of Collisions

40. Types of Collisions

41. Types of Collisions

42. Types of Collisions