1. Newton’s 3rd Law

2. Newton’s 3rd Law
Forces always exist in pairs

3. Examples of Newton’s 3rd Law
When you walk across the floor:
you push against the floor and the floor pushes against you

4. For Every Action There is an Equal and Opposite Reaction
When two objects interact with one another, the forces they exert on each other are called action-reaction pairs

5. Action-Reaction Pairs
Whenever a force is exerted, there is another force that is equal in size and opposite in direction
This is true even if there is no motion

6. Person Pushing Against a Wall

7. Force pairs do not always act on the same object
Even though the forces are equal and opposite, they do not cancel each other out because they act on different objects

8. Swimming
You push the water backward and the water pushes you forward

9. Hammer & Nail
Nail exerts a force on the hammer equal and opposite the force the hammer exerts on the nail
Net force acting on the nail, drives it into the wood

10. Rocket at Lift Off Action: rocket pushes on gas
Reaction: gas pushes on rocket

11. Equal Forces don’t always have equal effects
Because of Newton’s second law (F=ma) , an object’s mass will have an impact on the acceleration from the force

12. For Example
When a gun is fired, the force exerted on the bullet is as great as the reaction force exerted on the gun. Why is the recoil not at the same speed as the bullet?

13. These forces depend on friction
A person or car on ice may not be able to exert the action force to produce the needed reaction force