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Newtons 3rd Law of Motion

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Title: Newtons 3rd Law of Motion


1
Newtons 3rd Law of Motion
2
What is Newtons 3rd Law of Motion?
  • For every action, there is an equal and opposite
    reaction.
  • Example
  • Ice skaters pushing off each other sending them
    to opposite sides of the rink

3
Where does Newtons 3rd Law occur?
  • Everywhere!
  • Examples
  • Walking you push on the ground and the ground
    pushes back on you
  • Hitting a hammer hit the nail and the nail
    pushes back on the hammer

4
Can action and reaction forces cancel out? Why?
  • No, they cant cancel each other out because they
    are in opposite directions they cant be added
    together because they involve different objects.
  • Example 2 balls hitting each other then
    bouncing back

5
What is momentum?
  • Its a measure of the quantity of motion.
  • Its the product of the objects mass and its
    velocity.

6
How do we calculate momentum?
  • Momentum
  • Momentum mass x
  • Momentum mass x distance
  • time

mass
velocity
x
distance time
7
What are the units of momentum?
  • Remember momentum mass x distance
  • time

Momentum
kg
m
x
s
8
What can change momentum?
  • A change in
  • A change in
  • A change in
  • A change in

velocity
speed
direction
mass
9
  • A blue car is moving at 40 km/h and a red car is
    moving at 50 km/h. The blue car has a mass of
    2000 kg and the red car has a mass of 1200 kg.
    Which car has the greater momentum?

Momentumb
2000 kg x 40 km/h
80,000 (kgkm)/h
Momentumr
1200 kg x 50 km/h
60,000 (kgkm)/h
10
  • A train is traveling down the track at 30 km/h.
    It has a momentum of 300,000 kg-km/h. What is
    the mass of the train?

Momentum mass x velocity
300,000 kg-km/h mass x 30 km/h
300,000 kg-km/h mass 30 km/h
10,000 kg mass
11
  • A golf ball travels at 16 m/s and a baseball
    travels at 7 m/s. The mass of the golf ball is
    0.045 kg and the mass of the baseball is 0.14 kg.
    Which has the greater momentum?

Momentumg
0.045 kg x 16 m/s
0.72 (kgm)/s
Momentumb
0.14 kg x 7 m/s
0.98 (kgm)/s
12
  • Which has more momentum, a 250 kg dolphin
    swimming at 6 m/s or a 450 kg manatee swimming at
    2 m/s?

Momentumd
250 kg x 6 m/s
1500 (kgm)/s
Momentumm
450 kg x 2 m/s
900 (kgm)/s
13
Conservation of Momentum
  • The Law of Conservation of Momentum states that
    the total momentum of the objects doesnt change
    when they interact, unless outside forces act on
    the objects.

14
Scenario 1
  • What happens to the momentum of two moving
    objects when they hit?
  • The total momentum stays the same momentum is
    conserved.
  • The velocities of the objects may change, but the
    total momentum is the same.

They hit
10 m/s
10 m/s
5 m/s
5 m/s
15
Scenario 2
  • What happens to the momentum of one moving object
    when it hits and bounces off a stationary object?
  • The total momentum stays the same momentum is
    conserved.
  • The source of the momentum changes.

stopped
stopped
They hit
10 m/s
10 m/s
0 m/s
0 m/s
16
Scenario 3
  • What happens to the momentum of one moving object
    when it connects to a stationary object?
  • The total momentum stays the same momentum is
    conserved.
  • The mass being moved increased when joined
    together, but velocity decreases.

stopped
They connect
10 m/s
5 m/s
5 m/s
0 m/s
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