Momentum

1
Momentum
2
Momentum inertia in motion
3

• Moving object has large momentum if
• Mass is large (ship moving at slow speed)or
• Velocity is large (bullet moving at rapid
  speed)or
• Mass and Velocity are large (massive truck
  rolling down a steep slope with no brakes)

4

• What is the momentum of the truck if it is NOT
  moving?

5

• Why are the engines of supertankers turned off
  when they are 25 km from port?

6

• Changes in momentum may occur
• a change in the mass of an object
• a change in velocity,
• or both.

7

• If momentum changes but mass doesnt
• velocity changes..AND
• acceleration occurs.
• What produces an acceleration?
• FORCE
• bigger Force ? bigger ? in velocity ? bigger ? in
  momentum

8
Collisions

• Elastic
• colliding objects rebound without deformation or
  generation of heat
• Colliding objects BOUNCE OFF OF EACH OTHER!
• Inelastic
• Colliding objects become distorted, generate
  heat, and possibly STICK TOGETHER!

9
Elastic Collisions
Moving ball (green) strikes ball at rest
(yellow) Green ball stops, yellow ball moves away
Head-on collision Both balls bounce away
Two balls moving in same direction collide Green
moving faster than yellow Momentum transferred
from green ball to yellow Now yellow ball moving
faster
10
Inelastic Collisions

• Sticking together!

11
Inelastic Collisions

• Deformation.

12

• You are hovering (REST) next to the space shuttle
  in earth-orbit
• Your buddy of equal mass (moving at 4 m/s) (with
  respect to the ship) bumps into you.
• If she holds onto you, how fast do the two of you
  move after the collision?
• 2x mass in motion after collision? ½ v
• The 2 astronauts move together with a velocity of
  2 m/s after the collision.

13
Conservation of Momentum

• momentum before collision momentum after
  collision m1v1 m2v2

14
Big fishlittle fish
15
Big fish..little fish (part 2)
16

• Before collision, momentum of the loaded cart is
  150 kgcm/s momentum of the dropped brick is 0
  kgcm/s total system momentum is 150 kgcm/s.
• After the collision, momentum of the loaded cart
  is 90.0 kgcm/s momentum of the dropped brick
  is 60.0 kgcm/stotal system momentum is 150
  kgcm/s.
• The momentum lost by the loaded cart (60
  kgcm/s) is gained by the dropped brick.

17

• Before collision, momentum of the cart is 60
  kgcm/s momentum of the dropped brick is 0
  kgcm/s total system momentum is 60 kgcm/s.
• After the collision, momentum of the cart is
  20.0 kgcm/s momentum of the dropped brick is
  40.0 kgcm/stotal system momentum is 60 kgcm/s.
  
• The momentum lost by the loaded cart (40 kgcm/s)
  is gained by the dropped brick.

18

• Before the collision, momentum of the car is 20
  000 kgm/s momentum of the truck is 0
  kgm/stotal system momentum is 20 000 kgm/s.
• After the collision, momentum of the car is -10
  000 kgm/s momentum of the truck is 30 000
  kgm/stotal system momentum is 20 000 kgm/s.
• The momentum lost by the car (30 000 kgm/s) is
  gained by the truck.

19

• Before the collision, momentum of the truck is
  60 000 kgm/s momentum of the car is 0
  kgm/stotal system momentum is 60 000 kgm/s.
• After the collision, momentum of the truck is 30
  000 kgm/s momentum of the car is 30 000
  kgm/stotal system momentum is 60 000 kgm/s.
• The momentum lost by the truck (30 000 kgm/s)
  is gained by the car.

20

• Before the collision, momentum of the car is 20
  000 kgm/s momentum of the truck is -60 000
  kgm/stotal system momentum is -40 000 kgm/s.
• After the collision, momentum of the car is -10
  000 kgm/s momentum of the truck is -30 000
  kgm/stotal system momentum is -40 000 kgm/s.
• The momentum change of the car (-30 000 kgm/s)
  is equal in magnitude and opposite in direction
  to the momentum change of the truck (30 000
  kgm/s) .

21

• Before the collision, momentum of the car is 20
  000 kgm/s momentum of the truck is -60 000
  kgm/stotal system momentum is -40 000 kgm/s.
• After the collision, momentum of the car is -40
  000 kgm/s momentum of the truck is 0
  kgm/stotal system momentum is -40 000 kgm/s.
• The momentum change of the car (-40 000 kgm/s)
  is equal in magnitude and opposite in direction
  to the momentum change of the truck (40 000
  kgm/s) .

22
(No Transcript)
23
Sources

• http//www.physicsplace.com
• http//www.physicsclassroom.com/