1. Momentum Part 2
By: Heather Britton

2. Conservation of Momentum
The law of conservation of momentum states: The total momentum of an isolated system of bodies remains constant
By system we mean a set of objects that interact with each other
Isolated system means the only forces present are between the objects of the system

3. Conservation of Momentum
If two people on rollerblades push off of each other the momentum one person has will equal the momentum of the other person
Rockets are propelled by conservation of momentum
The “kick” from firing a gun is conservation of momentum

4. Conservation of Momentum
The law of conservation of momentum is very closely related to Newton’s third law of motion
When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first
The time the two objects are in contact is equal, so the change in momentum is equal but opposite (ΣFΔt = Δp)

5. Conservation of Momentum
Object 1 2
System
Initial momentum
p1o
p20
p1o + p20
Impulse
+FΔt
-FΔt
Momentum change
+Δp
-Δp
Final momentum p1 p2
p1 + p2

6. Conservation of Momentum
po = p
p10 + p2o = p1 + p2
m10v10 + m2ov2o = m1v1 + m2v2

7. Example 4
An astronaut at rest in space with a mass of 84 kg fires a thruster that expels 35 g of hot gas at 875 m/s. What is the velocity of the astronaut after firing the shot?

8. Collisions and Conservation of Momentum and Energy
In a collision the law of conservation of momentum holds true
The total momentum before the collision is the same as the momentum after the collision
The total amount of energy is conserved as well
Kinetic energy is not always conserved

9. Example 5
Glider A of mass kg moves along a frictionless air track with a velocity of m/s. It collides with gilder B of mass kg moving in the same direction at a speed of m/s. After the collision glider A continues in the same direction with a velocity of m/s. What is the velocity of glider B after the collision?