Momentum Crash Course

Transcription

1 Objective: To study momentum and its role in car crashes. Grade Level: 5-8 Subject(s): Science, Mathematics Prep Time: < 10 minutes Duration: One class period Materials Category: Household National Education Standards Science Mathematics Technology (ISTE) Technology (ITEA) Geography 2a, 3b, 3c 4a, 6a, 18b, 20a, 21c Materials (per group): Ruler with center groove Four marbles, same size Paper cup Scissors Two meter sticks Book to support track (3-4 cm thick) Related Link(s): Forces, Accelerations, And Car Accidents Supporting NASAexplores Article(s): The NASA/NASCAR Connection Page 1 of 3

2 Pre-lesson Instructions Students will be working in groups of three or four. Gather supplies for group activities. Background Information Motion and collision have been studied by scientists as far back as Isaac Newton. Through his studies and observations, he came up with three simple laws of motion. Newton s Second Law of Motion states that if you wish to accelerate something, you must apply a force to it. Newton s First Law of Motion then says, once an object is in moving, it will remain moving (unless friction or another outside force, like a wall, stops it). This is the inertia of motion, or momentum. An object s momentum is related to two things: the object s mass and velocity. If an object has a large mass, a large velocity, or both, it will have a large momentum. For example, a marble is much easier to stop than a bowling ball. Both have momentum, but the marble has less since it has less mass. Scientists who work with the National Association for Stock Car Racing (NASCAR) must pay special attention to momentum. Since racecars are heavy (large mass) and travel at high speeds (large velocity), their momentum is enormous. Special measures must be taken to protect the drivers inside. Many of NASCAR s safety precautions, such as better seat belts and car designs, were developed with the help of NASA scientists. Guidelines 1. Read the 5-8 NASAexplores article, The NASA/NASCAR Connection. 2. Tell the class that they will be learning about momentum and it s role in car crashes. Explain that momentum is the amount of oomph or bashing power of a moving object. Briefly discuss Newton s Laws of Motion. 3. Write the equation below on the board. momentum = mass x velocity 4. Distribute the Student Sheets and supplies to each group. Instruct each group to cut the section from their paper cup and to set up their ramp. This activity is best done on a long, flat table or on tile floors. Page 2 of 3

3 Discussion / Wrap-up Go over answers to the discussion questions on the Student Sheets. Answers: 1. Describe the relationship between the number of marbles hitting the cup and the distance the cup moves. As the number of marbles increases, the distance the cup moves also increases. The average increase in distance will vary. 2. What determines if one car has more momentum than another in a two-car crash? Momentum is a product of a car s velocity and mass. A lighter car can have a greater momentum if it has a higher speed compared with the heavier car. 3. Explain why an 80,000-pound semi-truck traveling 2 miles per hour (mph) has the same momentum as a 4, 000-pound Sport Utility Vehicle (SUV) traveling at 40 mph. Since momentum is the product of mass and velocity, the truck s large mass and slow speed is matched by the SUV s smaller mass but greater speed. momentum = mass x velocity p = mv Semi-truck s momentum = SUV s momentum mv = mv (80,000 lbs.)(2mph) = (4,000 lbs.)(40 mph) Discuss the students findings. Have the students put their weight (mass) into the equation to find their momentum when traveling in a car at 55 mph. Are they surprised? Extension(s) Have students perform more experiments with the same materials. Let them experiment with changing the ruler height and the distance from the end of the ruler to the cup. Students should learn that by increasing the starting height of the marble increases the velocity, and thereby increases the momentum. Explore the Law of Conservation of Momentum by studying the reactions of two colliding objects. Page 3 of 3

4 Materials (Per group) Ruler with center groove Four marbles, same size Paper cup Scissors Two meter sticks Book to support track (3-4 cm thick) Procedure 1. Cut a 3.0-cm-square section from the upper side of the paper cup. 2. Place the ruler with one end on the book and the other end resting on the desk. This ramp should start at a height of about 3-4 cm. 3. Place the cup upside down on the table or floor so that the opening cut from the side is resting on the ruler. 4. Place a meter stick along side the cup to measure the distance it moves. 5. Position one marble in the groove at the ruler s maximum height. 6. Release the marble, and observe the cup. 7. Measure the distance the cup moved (to the nearest 0.1 cm). 8. Perform three trials with just one marble, and record the results. 9. Repeat steps 5-8 using two, three, and four marbles at a time. 10. Average the results for each number of marbles, and record the data on the Data Sheet. 11. As a group, answer the questions on the Data Sheet. Page 1 of 2

5 Momentum Data Sheet measured distance cup moves (cm) Number of Marbles trial 1 trial 2 trial Average distance cup moves (cm) 1. Describe the relationship between the number of marbles hitting the cup and the distance the cup moves. 2. What determines if one car has more momentum than another in a two-car crash? 3. Explain why an 80,000-pound semi-truck traveling 2 miles per hour (mph) has the same momentum as a 4,000-pound Sports Utility Vehicle traveling at 40 mph. Page 2 of 2