RECALL: ANY change in velocity is due to an acceleration
VELOCITY is a SPEED with a DIRECTION
v1
v4
Fc
v2
v3
Centripetal Force: pulls an object moving at a constant
speed inward and results in circular motion
Newton’s Third Law of Motion
To every action force there is an equal and opposite
reaction force.
reaction
While the forces are
balanced, the motion that is
observed depends upon the
masses of the objects
involved.
(Rocket vs. exhaust gases)
action
Momentum: how much force is needed to change an
object’s motion
1. What is the momentum of a car with a mass of 1300 kg
traveling at a speed of 28 m/s?
p = mv = (1300 kg)(28 m/s) = 36,400 kg•m/s
2. What is the weight of the car in #1?
w = mg = (1300 kg)(9.8 m/s2) = 12,740 N
A few more examples:
1. A baseball thrown by a pitcher has a momentum of 6.0 kg•m/s.
If the baseball’s mass is 0.15 kg, what is the baseball’s speed?
p = mv
6.0 kg•m/s = (0.15 kg)v
v = 400 m/s
2. What is the mass of a person walking at a speed of 0.8 m/s if
their momentum is 52.0 kg•m/s?
p = mv
52.0 kg•m/s = m(0.8 m/s)
m = 65 kg
3. How fast must a 50 kg mass travel to have a momentum of
1500 kg •m/s?
p = mv
1500 kg•m/s = (50 kg)v
v = 300 m/s
4. If a 5000 kg mass is moving at a speed of 43 m/s, what is its
momentum?
p = mv
= (5000 kg)(43 m/s) = 21,500 kg•m/s
Law of Conservation of Momentum: Momentum can
be transferred from one object to another. In a closed
system, there is no gain nor loss of the total
momentum of all of the objects.