1. Teacher demonstration – please record:
Why did that happen?

2. Forces come in equal and opposite pairs
Can I touch your nose without your nose touching my finger?
Of course not!

3. 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”

4. Examples Balloon/air molecules Rocket ship/fuel molecules
Bike wheel/ground
Earth/Beyonce

5. 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?

6. 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?
Important point: equal and
opposite forces act on
DIFFERENT objects

7. If forces come in equal and opposite pairs, why do we often only see one object move?
2 kg
40 kg
2 N
2 N
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.)

8. 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

9. Balloon races Please, please, please…follow the instructions!!!!!!
Answer all questions in complete sentences

10. Tell me…
Why did that work?