1. Newton’s 3rd Law
Chapter 6

2. Forces Forces occur when two objects interact.
This consists of a push or pull on the object.

3. Forces Forces act in pairs. We call these pairs action-reaction pairs.
Action-reaction pairs are equal in magnitude but opposite in direction.

4. Forces When a force occurs, there are two objects being considered.
There are also two forces being considered.
One force acts on each object.

5. Newton’s 3rd Law
Newton’s 3rd Law states: Whenever one object exerts a force on a second object, the 2nd object exerts an equal and opposite force on the first object.

6. Newton’s 3rd Law
Simply put – For every action, there is an equal and opposite reaction.

7. Newton’s 3rd Law The first force is the action force.
The second force is the reaction force.
Action: A acts on B
Reaction: B acts on A

8. Newton’s 3rd Law [F=ma]1 = [F=ma]2
Think about a cannon and a cannonball.

9. Examples
What will be the acceleration of recoil when a 60 kg person on rollerblades pushes against a wall with a force of 30N ?

10. Answer
F=ma
Therefore a = F/m
30N/60kg = 0.5 m/s2 away from the wall

11. Examples
What is the net force on a falling 1000N barrel hitting a pavement with 5000N of force?

12. Answer Fnet = result of all forces combined.
Fnet = 5000 N – 1000 N = 4000 N upward.