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

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1 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 CONCEPT REVIEW QUESTIONS /18 4. WS READING GUIDE PP /37 5. WS MATH / CONCEPT PRACTICE WORKSHEET /44 6. LB Balloon propelled Car Lab (Group Lab) /25 7. LB EGG CAR LAB (Lab Report) /25 APPLICATION REPORT /25 Participation points (see handout) up to 50 points /50

2 5 points for filling in all the notes 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: Write at least 5 study questions From the notes (5 points) 2 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 3 5 points for filling in all the notes 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. Write at least 5 study questions From the notes (5 points) is also important. - how long you apply the force The longer the force is applied, the greater the change in Newton s 2 nd law says: We also know that acceleration = If you plug the acceleration formula into the 2 nd law you get: Rearrange the formula and you get: 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

4 5 points for filling in all the notes Write at least 5 study questions From the notes (5 points) Case 3 - Decreasing momentum over a short time 4 If the time is short, then you need a force to change the momentum 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 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 WORKSHEET (17 PTS ) 5

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7 7 CONCEPT REVIEW WORKSHEET /18 (use your PowerPoint notes to help with this worksheet) 1. a. What is Newton s 3 rd Law? (1pt) b. Give 2 examples of the 3 rd law. (2pts) 2. a. Which has the greater mass - a heavy truck at rest or a toy car rolling down the sidewalk? (1pt) b. Which has the greater momentum? (1pt) 3. a. Write the formula for Impulse. (1pt) b. If you increase the time that the same force is applied to an object, (apply the force over a longer time) does this increase or decrease the impulse? (1pt) c. Will this give more or less change in momentum? (1pt) 4. In a car crash, why is it good for the driver to extend the time during which the collision is taking place? (1pt) 5. If the time of impact in a collision is extended by four times, by how much is the force of impact changed? (1pt) 6. a. What is the law of conservation of momentum? (1pt) b. In terms of momentum conservation, why does a gun kick(recoil) when fired? (1pt) 7. a. What is an elastic collision? (1pt) b. Give an example of an elastic collision. (1pt) 8. a. What is an inelastic collision? (1pt) b. Give an example of an inelastic collision. (1pt) 9. 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? (1pt) 10. Why are you hurt less if you fall on a floor with "give" than on a rigid floor? (1pt)

8 8 READING GUIDE 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)

9 9 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)

10 10 MATH and CONCEPT PRACTICE WORKSHEET /44 pts 1. A person pushes on a large box with a force of 500 N. The box does not move. Draw a vector diagram (with arrows) to show this situation. (1pt) How much force does the box push back on the person? (1pt) 2. A light hanging from a chain on the ceiling weighs 40 N. Draw a vector diagram to show this situation. (1pt) How much force does the chain exert on the light? (1pt) 3. When a 160 pound man steps from a 20 ton cruise ship onto a dock, the only apparent movement is the man s, the ship doesn t seem to move. However if he steps off a rowboat onto a dock, he may fall into the water if the boat is not tied up securely. Explain why these situations are different using the law of conservation of momentum. (1pt) 4. An astronaut with a mass of 60 kilograms and a satellite with a mass of 1230 kilograms are weightless in space and right next to each other. The astronaut pushes on the satellite with a force of 35 Newtons. A. How much force does the satellite push back on the astronaut? (1pt) B. Determine the acceleration of the astronaut. (4 pts formula, work, answer, label) C. Determine the acceleration of the satellite (4 pts formula, work, answer, label) 5. A father and his 6-year old daughter are facing each other on ice skates. With their hands, they push off against one another. A. What can be said about the force on the father and the force of the daughter? (1pt) B. Which one will experience the larger acceleration? (1pt)

11 6. A rope is used in a tug-of-war between two teams of five people each. Both teams are equally strong so neither team wins. If you tie one end of the rope to a tree that doesn't move, how many people will you need to generate the same magnitude of force by pulling on the tree that the competition had? Draw a vector diagram and explain your answer. (2pts) A. A car with a mass of 1200 kg moves at a speed of 90 km/hr. What is it s momentum? (4 pts formula, work, answer, label) B. Another car has the exact same momentum, but only a mass of 800 kg. What speed is it traveling? (4 pts formula, work, answer, label) 8. A net force accelerates a 75 kg skier from 1.0 m/s to 6.5 m/s over a time interval of 20 seconds. A. Find the initial momentum and final momentum of the skier. (4 pts answer, label for each) B. What is the change in momentum? (1pt) C. Using the formula F = ΔP Find the Force acting on the skier to cause the acceleration. t (3 pts work, answer, label) 9. Coal is transported to electrical generating plants in railroad cars. An empty coal car with a mass of 9000 kg coasts at a speed of 2.5 m/s. An 18,000 kg load of coal with no horizontal velocity is dropped into the car. A. What is the momentum of the empty coal car? (4 pts formula, work, answer, label) B. What is the momentum of the coal before it drops? (1pt) C. What must be the total momentum of the car after the coal combined with it? (1pt) D. At what speed does the car and coal combination coast? (4 pts formula, work, answer, label)