Name Period CHAPTER 7 NEWTON'S THIRD LAW OF MOTION MOMENTUM & CONSERVATION OF MOMENTUM ACTIVITY LESSON DESCRIPTION POINTS

Transcription

1 Name Period CHAPTER 7 NEWTON'S THIRD LAW OF MOTION MOMENTUM & CONSERVATION OF MOMENTUM ACTIVITY LESSON DESCRIPTION POINTS 1. NT OVERHEAD NOTES WITH WORKSHEET GUIDE /30 2. WS MOMENTUM WORKSHEET /17 3. WS MOMENTUM REVIEW QUESTIONS /20 4. WS READING GUIDE PP /37 5.? S CHAPTER QUESTIONS PP Do #1 (2pts) #5 a,b (8 pts) #6 a,b (8pts) #9 (2pts) #11 (4pts), #12 (2pts) and #13 (4pts) /30

2 NEWTON'S THIRD LAW States that: Whenever one object exerts a force on a 2 nd object the 2 nd object exerts an equal and opposite force on the first. Or in other words: ACTION/REACTION ON DIFFERENT MASSES When a rifle is fired, there is an interaction between the rifle and the bullet - the force the rifle exerts on the bullet is exactly and to the force the bullet exerts on the rifle - and the rifle kicks. So why does the bullet go so fast, or why doesn't the rifle kick more? According to Newton's second law: The forces are equal, but the mass is. The bullet has a large because of a small The gun has a acceleration because of a mass. MOMENTUM Momentum means, or the mass of an object multiplied by its velocity. MOMENTUM = A truck rolling down a hill has more momentum than a skate rolling at the same speed, because

3 If the momentum of an object changes, either the mass or the velocity, or both must change. Usually the mass does not change. To change the velocity, a must act on the object. The greater the force, the greater the change. is also important. - how long you apply the force The longer the force is applied, the greater the change in The force x time is called Case 1 - Increasing momentum Apply the greatest we can over the period of Case 2 - Decreasing momentum over a long time If the time is long, then you need a force to change the momentum Case 3 - Decreasing momentum over a short time If the time is short, then you need a force to change the momentum

4 BOUNCING - Impulses are greater when something bounces because: Example: Pelton Paddle Wheel was a curved wheel used in the California gold rush. The curved wheel allowed the water to, producing a greater, so more momentum. Pelton became rich from his invention, not the gold. THE LAW OF CONSERVATION OF MOMENTUM: States that in the absence of an external force, the momentum of a system remains. Example: The momentum of a rifle is zero before it is fired. After firing, the net momentum must still be zero. The momentum of the bullet is: The momentum of the gun (the kick or recoil) is: The two momentums are equal and opposite, so they cancel out and the net momentum is still zero. ELASTIC COLLISIONS: When objects collide without lasting deformation or the generation of heat. They bounce apart. INELASTIC COLLISIONS: Whenever colliding objects become entangled or hooked together.

5 MOMENTUM - REVIEW WORKSHEET 1. a. Which has the greater mass - a heavy truck at rest or a rolling skateboard? b. Which has the greater momentum? 2. When the average force of impact on an object is extended in time, (so the same force but more time) a. Does this increase or decrease the impulse? b. Will this give more or less change in momentum? 3. In a car crash, why is it good for the driver to extend the time during which the collision is taking place? 4. If the time of impact in a collision is extended by four times, by how much is the force of impact changed? 5. Why is the force of impact greater in a collision that involves bouncing? 6. In terms of momentum conservation, why does a gun kick (recoil) when fired? 7. What is the difference between an elastic and inelastic collision? 8. You can't throw a raw egg against a wall without breaking it, but you can throw it with the same speed into a sagging sheet without breaking it. Explain why? 9. Why are you hurt less if you fall on a floor with "give" than on a rigid floor? 10. Who suffers the most harm - a person who comes to an abrupt halt when he falls onto pavement, or a person who bounces as they hit? Explain.

6 pp An object s tells you how much inertia it has (1) 2. Objects in motions have also (1) 3. An objects momentum tells you what? (1) 4. Why is a fast moving softball harder to catch than a slow moving one? (1) 5. Why is an iron shot harder to catch than a softball at the same speed? (1) 6. Write the equation for linear momentum and tell what each letter stands for. (2) 7. What are the SI and English units for momentum? (2) 8. Write the formula for Newton s 2 nd law learned in chapter 4. (1) 9. Write an alternate equation of Newton s 2 nd law using momentum and tell what the letters mean. (3) 10. State the alternate form of Newton s 2 nd law with words. (1) 11. To change the speed and momentum of an object, a force must be applied for what? (1) 12. What is Impulse? (1) 13. Write the English and SI units for impulse/ (2) 14. Impulse explains the importance of in many sports. (1)

7 15. Look at Example 7.3 then solve the following: In a penalty kick, a soccer player increases the speed of a ball from 0 to 30 m/s. The mass of the soccer ball is 0.45 kg. a) What impulse does the soccer player give the ball? (4) b) If the player s foot is in contact with the ball for 0.14 seconds, what is the average force exerted on the ball? (4) 16. A force is an between 2 objects (1) 17. State Newton s 3 rd Law of Motion (1) 18. Newton s 3 rd law says that forces always come in, sometimes called and forces (3) 19. A closed system on which no net external forces act is called what? (1) 20. No matter what internal interactions take place in a closed isolated system, its linear momentum (1) 21. State the Law of Conservation of Momentum (1) 22. When you use conservation of momentum to solve a problem, what 2 things do you need to define the system boundary? (2)

8 SECTION EXERCISES PP /30 #1 (2pts) #5 a. (4 pts) b. (4 pts) #6 a. (4 pts) b (4 pts) #9 (2pts) #11 (4pts) #12 (2pts) #13 (4pts)