1. Newton’s 3rd Law

2. How a force on an object affects other objects.
Newton’s 1st Law
How an object behaves when there is NO net force acting on it.
Newton’s 3rd Law
How a force on an object affects other objects.
Newton’s 2nd Law
How an object behaves when there is a net force acting on it.

3. Newton’s 3rd Law
When one object exerts a force on another object, the second object exerts a force of equal size on the first object in the opposite direction.

4. 1. A book pushes on a table with a force of 12N
1. A book pushes on a table with a force of 12N. The table pushes ______________ on the book with a force of _____________.
upward
12N
2. A hand pushes on a spring with a downward force. The _____________ pushes on the _____________ with an ________________________.
spring
hand
Upward 40N force

5. 3. A girl’s weight _________________ with a ______________ of 600N
3. A girl’s weight _________________ with a ______________ of 600N. The rings _____________________ with a ____________ of _____________.
Pulls downward
Force
Pull upward
force
600N

6. 4. The action force is the car tires pushing on the ground.
The reaction force is the ground pushing on the car tires.

7. 5. The action force is the rocket pushing on the gas.
The reaction force is the gas pushing on the rocket.

8. 6. The action force is the earth pulling down on the ball.
The reaction force is the ball pulling up on the earth.

9. 7. As you stand on a floor, the floor exerts an upward force on your feet. Why don’t you accelerate upward from this force?
Your weight and the normal force of the floor pushing up on you are equal but in opposite directions. They cancel out to zero, so you don’t accelerate.

10. 8. A girl hangs from the ends of the rope as shown in the figure
8. A girl hangs from the ends of the rope as shown in the figure. If gravity pulls her downward with a forceof 500N, what is the reading on the force scale near her left hand?
250N
250N
250N
The sum of the upward forces (250N + 250N) must equal the sum of the download forces (500N).

11. What is the opposite force from Newton’s 3rd Law?
The downward force of a hammer on a nail.
The upward force of the nail on the hammer.

12. What is the opposite force from Newton’s 3rd Law?
The force of gravity pulling down on a book.
The force of gravity pulling up on the earth.

13. What is the opposite force from Newton’s 3rd Law?
The force of helicopter blades pushing air down.
The force of air pushing helicopter blades up.

14. What is the opposite force from Newton’s 3rd Law?
The force of air resistance on a thrown baseball.
The force of the baseball pushing forwards on the air.

15. 10. In each of the situations shown in the figures below, does the force scale read 0N, 100N, 200N, or something else? Why?
100N, The total force to the right of the spring scale 100N.
100N, These two situations are identical as far as the spring scale is concerned.