1. STARTER Imagine a loaded shopping cart and a small glass marble are both slowly rolling toward you at the same speed. The marble is easier to stop. Intuitively, you know that a loaded shopping cart is harder to stop because it has a greater mass. If the marble were moving 100 times faster than the shopping cart, which would be easier to stop? Why do you think this concept is?

2. NEWTON’S THIRD LAW: ACTION-REACTION Day 18

3. INQUIRY MINI-LAB Momentum Materials needed: Marbles rulers Answer questions and fill in the chart

4. NEWTON’S THIRD LAW For every action there is an equal and opposite reaction.

5. WHAT DOES THIS MEAN? For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

6. THINK ABOUT IT... What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

7. WHY DON’T THESE FORCES CANCEL OUT? Action and reaction forces don’t cancel out. Why? The reason is because that action and reaction forces don’t act on the same object. For example: A swimmer in the water. The action force acts on the water but the reaction force acts on the swimmer.

8. EXPLAIN: NEWTON’S 3 RD LAW Directions: Identify the action and reaction in each picture?

9. MORE EXAMPLES You push on floor, the floor pushes on you Car pushes on road, the road pushes on the car Swimming – you push water backward, the water pushes you forwards More friction – more force

10. MOMENTUM How can a karate expert break a stack of bricks? Why does it hurt more to fall on concrete than a wooden floor? Why do you follow through in golf, baseball or bowling?

11. MOMENTUM Momentum is a property of moving matter. Momentum describes the tendency of objects to keep going in the same direction with the same speed. Changes in momentum result from forces or create forces. Momentum is the product of an object’s mass and its velocity. An object has a large momentum if the product of its mass and velocity is large.

12. MOMENTUM AND INERTIA Inertia is another property of mass that resists changes in velocity; however, inertia depends only on mass. Inertia is a scalar quantity. Momentum is a property of moving mass that resists changes in a moving object’s velocity. Momentum is a vector quantity.

13. CALCULATING MOMENTUM  The momentum of a moving object is its mass multiplied by its velocity.  That means momentum increases with both mass and velocity. Velocity (m/sec) Mass (kg) Momentum (kg m/sec) p = m v

14. CONSERVATION OF MOMENTUM The law of conservation of momentum states when a system of interacting objects is not influenced by outside forces (like friction), the total momentum of the system cannot change. If you throw a rock forward from a skateboard, you will move backward in response.

15. EXPLORE: MOMENTUM Directions: Write the following scenario. As a Group, answer the question. A 62.1-kg male ice skater is facing a 42.8-kg female ice skater. They are at rest on the ice. They push off each other and move in opposite directions. The female skater moves backwards with a speed of 3.11 m/s. The male skater moves with a speed of 2.14 m/s. Which skater has the greater momentum and why?

16. PRACTICE PROBLEMS KWFL CHART: MOMENTUM Directions: In your notebook, do a KWFL chart for the following problems. You can work with each other as long as you have your own problems. I will check answers. 1. What is the momentum of a 3000 kg truck going 55 m/s? 2. What is the momentum of a 99 kg boulder going 30 m/s? 3. What is the momentum of a 1000 kg car going 25 m/s? 4. What is the momentum of a 500 kg object going 70 m/s?

17. EXIT SLIP List three examples of Newton’s Third Law. Turn in Lab. Make sure to answer questions.