Chapter 2 – Lesson 4

1. Chapter 2 – Lesson 4

2. Newton’s Third Law of Motion For every action there is an equal and opposite reaction. When one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object. ANOTHER WAY TO SAY IT….

3. Think about it… PUSHES PUSHES BACK SAME LENGTH OPPOSITE How is the gymnast able to flip over? When the gymnast the vault, the vault against the gymnast. The of the force arrows are the but the direction is

4. Force Pair OPPOSITE DIRECTIONS THE BOAT THE GIRLS FEET The forces two objects apply to each other. Force pairs will always act in The girls feet act on The boat acts on

5. Do Action-Reaction Forces Cancel? DO NOT 2 DIFFERENT OBJECTS If 2 equal act in opposite directions they are balanced and cancel each other out. There is no movement Action – Reaction forces cancel out because they are acting on

6. FORCE PAIR MASSIVE MOVE LESS MASSIVE If one of the pairs is much more you will only see the object Example – When you push down on the Earth, you won’t see the Earth move, only you jumping in the air

7. ACTION AND REACTION FORCE PAIR ACTION FORCE REACTION FORCE ACTION FORCE EQUAL REACTION FORCE OPPOSITE ACT ON DIFFERENT OBJECTS In a one force is called the and the other force is called the For every there is a that is in strength, but in direction. Action – Reaction forces don’t cancel because they

8. How do Action-Reaction forces work when you are… • When you jump, you push down on the ground. • The ground then pushes up on you. It is this upward force that pushes you into the air. JUMPING

9. How do Action-Reaction forces work when… • *When the rocket fuel is ignited, a hot gas is produced. As the gas molecules collide with the inside engine walls, the walls exert a force that pushes them out of the bottom of the engine. THE DOWNWARD PUSH • The action force is - THE UPWARD PUSH ON THE ROCKET ENGINE BY GAS MOLECULES • The reaction force is - A rocket launches

10. Why doesn’t the bowling ball move backward if the pin is pushing on it equally? MOMENTUM The bowling ball has more

11. Momentum MASS VELOCITY m v kg m/s kg * m/s The measure of how hard it is to stop a moving object. Momentum = x P = x Units: Mass = Velocity = Momentum =

12. Momentum MASS MOMENTUM VELOCITY MOMENTUM MOMENTUM GREATER FORCE STOP More = more More = more More = needed to an object. Which object would have more momentum?

13. Practice Problem 1 What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s?

14. Practice Problem 2 A golf ball travels at 16m/s, while a baseball moves at 7 m/s. The mass of the golf ball is .045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum?

15. Law of Conservation of Momentum MOMENTUM VELOCITY & MOMENTUM MOMENTUM The total momentum of a group of objects stays the same unless outside forces act on the objects. The cue ball has because it has mass and velocity. When it hits the other balls , the cue balls decrease. The other balls start moving (and have mass) which mean they now have

16. Collisions When colliding objects bounce off each other When objects collide and stick together. always be the same after the collision. Objects collide in two different ways: Elastic collision – Inelastic collision – The amount of momentum involved before the collision will

17. Collisions with 2 moving objects SAME DIRECTION COLLISION SPEEDS UP SLOWS DOWN BEFORE COLLISION 4 m/s 2 m/s AFTER COLLISION When two objects are moving in the and a occurs, the momentum of the slower object and the momentum of the faster object

18. Collisions with 1 moving object COLLIDES ONE MOMENTUM TRANSFERRED NONMOVING BEFORE COLLISION 4 m/s 0 m/s AFTER COLLISION When object is moving and into a nonmoving object, all the is to the object.

19. Collisions with connected objects COLLIDES CONNECTS MOMENTUM TWO MOVING OBJECTS BEFORE COLLISION 0 m/s 4 m/s AFTER COLLISION When one object is moving and , but to a nonmoving object, the gets evenly split between the