Transcript Newton`s 3rd Law and Momentum

rd
3
Newton’s
Law
and Momentum
Chapter 10 Section 4
Newton’s
rd
3
Law of Motion
If one object exerts a force on another object,
then the second object exerts a force of
equal strength in the opposite direction.
What does that mean?
For every ACTION…there is an equal and
opposite REACTION!
Action-Reaction Pairs
When the gymnast
does a flip, she
pushes
down on the vaulting
horse (action force).
The reaction force of
the vaulting horse
pushes her up to
complete the flip.
Do Action-Reaction Forces cancel
each other out?
NO!
The Action-Reaction Forces act on different
objects.
Momentum!
Quantity of Motion
Momentum = Mass x Velocity
Kg x m/s
Momentum is a vector quantity
Momentum of an object is in the same
direction as its velocity

If a bicycle and a fire engine are both moving
at a speed of 5 km/hr, which would be easier
to stop? Why?
The Bicycle! It has less mass, and therefore, has less
momentum. Momentum = Mass x Velocity

When a car slows down, its velocity decreases
and its mass stays the same. How does
slowing down affect the car’s momentum?
The Momentum Decreases! Momentum= Mass x Velocity!
Math Practice
Turn to Textbook page 396 “Math Practice”
and complete problems #1-2. Show
equation and work!
Conservation of Momentum
What does Conservation Mean?
The total momentum of any group of objects
that interact (collide) remains the same
(conserved) unless acted on by some outside
force.
What is an example of an outside force?
Friction!
SEE OVERHEAD
FOR PICTURES OF
DIFFERENT TYPES OF
COLLISIONS