1. Newton’s Third Law of Motion Action and Reaction

2. Questions I should be able to answer when we are done What is Newton’s 3 rd law? What are force pairs? Force pairs are always ______ and ______? When do force pairs cancel each other out? When do they not? What do force, mass, and acceleration have to do with Newton’s 3 rd law?

3. Question: Is it possible for me to touch the table but not have the table touching me?

4. Forces and Interactions A force is a push or pull. Forces do not act alone. Forces are mutual actions called INTERACTIONS between two things.

5. For example… A hammer hits a nail… The nail interacts with the hammer. The hammer hits the nail and the nail hits the hammer.

6. Newton’s Third Law “Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first”

7. In other words… “For every action there is an EQUAL and OPPOSITE reaction”

8. Action vs. Reaction For example: One Force (an action): Pushing on a wall Second Force (a reaction): The wall pushing back

9. What happens to you when you jump off a boat onto the shore? What happens to the boat?

10. Action and Reaction “ACTION” happens first: Driving in a car, the tires push on the road. Dropping a book, the Earth pulls on the book. “REACTION” happens second: The road pushes back on the tires. The book pushes back on the Earth.

11. Action and Reaction on Different Masses FORCES are equal even if MASSES are different.

12. Action and Reaction on Different Masses The force exerted on a cannon is equal to the force exerted on the cannonball So, why does the cannonball move so much faster and farther than the cannon?

13. Why don’t they cancel each other out? Do the action and reaction act on the same object? If so, they can cancel each other out.

14. Action VS Reaction Equal in magnitude and opposite in direction Forces do not cancel each other out.

15. The Horse-Cart Problem Observe the pairs of forces acting on the horse and cart

16. ACTION = REACTION Example: Pushing on a wall vs Punching a wall

17. Vocabulary 1. action force3. Newton’s 3 rd Law 2. interaction4. reaction force

18. Questions I should be able to answer when we are done What is Newton’s 3 rd law? What are force pairs? Force pairs are always ______ and ______? When do force pairs cancel each other out? When do they not? What do force, mass, and acceleration have to do with Newton’s 3 rd law?