2. Newton’s Third Law of Motion: Every action has an
equal and opposite reaction.
This means that all forces work in pairs and every time
an object exerts a force on a second object, the second
object exerts a force back on the first object that is equal
in strength and opposite in direction.

3. Action: If you hit a nail
with a hammer, the
hammer pushes the nail
into the wood.
Reaction: The nail also
pushes back on the
hammer which causes
its motion to stop
suddenly when it hits. Action: You are standing
on a skateboard and you
throw a ball.
Reaction: You will roll in
the opposite direction of
the ball with a force equal
to the force applied to the
ball.

4. Action: If you sit on
a chair, you push
down on the chair.
Reaction: The chair
pushes back on you
Do Action and Reaction Forces Cancel?
Remember that balanced forces that are
equal and opposite cancel and the net
force is zero.
Yet, the action/reaction forces in Newton’s
third law do not cancel. This is because
the action and reaction are not acting on
the same object and cannot be added.

5. Forces Acting on Bucket
Action Reaction Pairs
Hand on
bucket
Bucket on
hand
Earth on
bucket
Bucket on earth
Net
force on
bucket
• Action and reaction forces are always balanced.
• One force does not cause the other, they exist at the
same time.
• Either force could be called the action and the other
force is the reaction.
• If action and reaction forces are always balanced, how
can there be any motion? Notice that action/reaction
forces act on different objects. If you look only at the
total forces on one object you find forces that may or