Download Slide 1

http://www.sciencewithmrnoon.com/projectarise/phy
sics1st/newtoncradle.swf
Whenever one object exerts a force on a
second object, the second object exerts
an equal and opposite force on the first
object
For every action, there is an equal
and opposite reaction
Newton’s Third Law of
Motion
Newton’s third law states that
for every action force there has
to be a reaction force that is
equal in strength and opposite
in direction.
One force is called the action force
The other force is called the
reaction force
The action and reaction forces are
equal in strength and opposite in
direction
Forces always come in pairs
All forces come in pairs. When
you push on the ground (action), the
reaction of the ground pushing back on
your foot.
It does not matter which force you call
the action or the reaction. The action and
reaction forces are interchangeable.
DISCUSSION
Does a stick of dynamite contain
force?
DISCUSSION
No. Force is not something an
object has, it is an interaction
between one object an another
DISCUSSION
A car accelerates along a road.
Strictly speaking, what is the force
that moves the car?
DISCUSSION
The road pushes the car along! The
rotating tires push back on the road
(action) and at the same time the road
pushes forward on the tires (reaction)
Discussion:
When a cannonball is shot out of a
cannon, the force exerted against the
cannon is the same force that drives the
cannonball. Why then does the
cannonball undergo more acceleration?
How does the space shuttle
get into space?
The shuttle's action is to push
down on the ground with the
force of its powerful engines,
and the reaction is that the
ground pushes the rocket
upwards with an equal force.
An astronaut can move in space by
throwing an object in the direction opposite
where the astronaut wants to go.
While driving down the road, a firefly
strikes the windshield of a bus and
SPLAT! This is a clear case of Newton's
third law of motion. The firefly hit the
bus and the bus hits the firefly. Which
of the two forces is greater: the force on
the firefly or the force on the bus?