Lab: Applications of Newton s Second Law of Motion Purpose: To investigate the relationship between force and acceleration mathematically, then using an Atwood machine verifying our calculations. Equipment: 1 Atwood machine 1 Sonic Ranger 14 10g masses Name: Lab Partners: REMOVE THIS COVER SHEET FROM THE LAB PACKET AND REPORT ALL DATA COLLECTED USING THE TABLES BELOW Weight = mass x 9.8m/s Trial 1 3 4 Mass block 1 Weight block 1 Mass block Weight block Mass difference Trial acceleration calculated acceleration experimental Difference calculated - experimental 1 3 4
Applications of Newton s nd Law: Procedure: 1. Set-up the Atwood machine as illustrated in the diagram below.. In the space provided below, create free body diagrams that illustrate all the forces acting on the hanging masses. 70 kg 70 kg 3. Describe your observations using appropriate vocabulary. Student answers should indicate that the forces acting on the system are balanced so there is no acceleration. 4. Using Newton s second law, write an equation that shows the net forces acting on the system. Remember to system. The equation should match your description from number 3 and your free body diagram. F = ma - = a(m 1 m ) -0.686N 0.686N = a(0.140kg) 0N /0.140kg = a a = 0 m/s 5. Next, make a prediction about what would happen if you were to increase the mass on one side of the Atwood machine. (i.e. take a 10-gram mass from the right side and add it to the left side) Student answers should indicate that by increasing the mass on one side, the net forces are no longer balanced. This will lead to an acceleration of the system.
6. Visualize the system and draw another set of free body diagrams to illustrate what the system will look like. 7. Using Newton s second law, write an equation that shows the net forces acting on the system. Remember to system. The equation should match your description from number 5 and your free body diagram. F = ma - = a(m 1 m ) -0.784N 0.588N = a(0.140kg) -0.196N /0.140kg = a a = -1.40 m/s 8. You now have a theoretical model of how your system should behave. Now transfer one 10g mass from one side of the Atwood Machine to the other. Pull the smaller set of masses down so that the larger set is as high as the string will allow. Use the sonic ranger and data logger to measure the acceleration of the larger set of masses. Be sure to press the collect button on the data logger problem before you release the larger set of masses. Record your data. 9. How does your measured value compare to your calculated value? If there are differences, try to account for 10. Add another 10 grams to the side that you already increased the mass on. Make a prediction about what should happen next, will the acceleration be the same? Explain why or why not. Student responses should indicate that the forces acting on the system will now be out of balance and that an acceleration will result.
11. Draw free body diagrams for the system. 1. Using Newton s second law, write an equation that shows the net forces acting on the system. Remember to system. The equation should match your description from number 10 and the free body diagram. F = ma - = a(m 1 m ) -0.8N 0.490N = a(0.140kg) -0.39N/0.0140kg = a a = -.80 m/s 13. You now have a theoretical model of how your system should behave. Next set up the sonic ranger so that it can log the motion of your system. Use the data logging software to measure the acceleration of the system. Record your data. 14. How does your measured value compare to your calculated value? If there are differences, try to account for 15. Add another 10g to the machine (again to the side that you have already been loading). Make a prediction about what should happen next, will the acceleration be the same? Explain why or why not. Student responses should indicate that the acceleration would be greater because of a greater imbalance of the forces acting on either side of the system.
16. Draw a free body diagram of the system. 17. Using Newton s second law, write an equation that shows the net forces acting on the system. Remember to system. The equation should match your free body diagram. F = ma - = a(m 1 m ) -0.980N 0.39N = a(0.140kg) -0.588N/0.014kg = a a = -4. m/s 18. You now have a theoretical model of how your system should behave. Next set up the sonic ranger so that it can log the motion of your system. Use the data logging software to determine the acceleration of the system. Record your data. 19. How does your measured value compare to your calculated value? If there are differences, try to account for 0. From your results make a statement about what happens to the acceleration of a system as the net force acting on the system changes. Student responses should indicate an understanding that as the forces acting on an object increases so does the acceleration of the object. 1. In reflection, discuss the impact that Newton s second law has on your everyday life. For example, the Atwood machine is essentially a pulley; can you think of any examples of a pulley and relate how Newton s second law applies to its function? Student responses will vary but should include at least one example of a pulley and some understanding of how Newton s second law applies to it. Write your reflection on the back of this page.