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Teacher demonstration – please
record:
• Why did that happen?
Forces come in equal and opposite
pairs
• Can I touch your nose without your nose
touching my finger?
Newton’s Third Law
• For every force on one object, there is an
equal and opposite force on another object
• “For every action there is an equal and
opposite reaction”
Examples
• Balloon/air
molecules
• Rocket ship/fuel
molecules
• Bike wheel/ground
• Earth/Beyonce
Example problem
A student pushes against a tree with a force of
10 newtons (N). The tree does not move. What
is the amount of force exerted by the tree on
the student?
Where are the equal and opposite
forces…
• When I lean against the wall?
• When I slap Ms. Hoang?
• When an 18-wheeler slams into a fly on the
highway going 70 mph?
If forces come in equal and
opposite pairs, why do we often
only see one object move?
2 kg
40 kg
2N
2N
Remember Newton’s 2nd Law? – each object will accelerate
(or change its velocity) differently depending on the object’s
mass. Apply the same force to 2 objects, and the object with
less mass will accelerate more. (Also remember, there are
usually multiple forces acting on an object.)
Bumper cars!
• What makes bumper cars so fun (and a little
dangerous)?
– Since forces come in equal and opposite pairs,
when I slam into another person’s car, that car
puts an equal and opposite force on my car, so I
feel a little whiplash
Balloon races
• Please, please, please…follow the
instructions!!!!!!
• Answer all questions in complete sentences
Tell me…
• Why did that work?