13 Lab 4 Tension and Friction Part A Tension and Weight 1. First make sure the air track is level. Use the air track, smart-pulley, and computer interface to measure the acceleration of the air cart pulled by the weight of three different masses: m = 20 g, 30 g, and 40 g . 2. Sketch a generalized free body diagram of the hanging mass. Remember: free body diagrams are sketches of ONE body and ALL forces acting on THAT body. 3. Apply Newton's 2nd law to the hanging mass. Use the resulting equation to solve for the tension in each of the three trials. 4. Now sketch a generalized free body diagram of the cart. Where is the normal force coming from in this case? 5. Apply Newton's 2nd law to the horizontal motion of the cart. Use the resulting equation to solve for the mass (M) of the cart for each of the three trials. Average these results and find the standard deviation. 6. Now measure the actual mass of the cart. How do the measured and calculated values compare? 7. Now, without actually setting it up, calculate the acceleration you would expect if the air cart were pulled by a mass of 25 g. Need a hint? Consider the equations from steps 3 and 5. These were results of applying Newton's second law to the motion of both objects. Combine these two equations and two unknowns to arrive at a formula for the acceleration. 8. Now, verify your answer by actually trying it out. Part B Tilted Air Track 9. Tilt the air track using wood blocks so that the pulley end of the track is highest. 10. Hang just enough mass from the string to hold the cart near the center of the inclined plane without motion (in equilibrium) while the air is turned on. What is the sum of the forces on the cart at this point? 11. Give the cart an initial velocity by gently pushing it down the track, and measure its acceleration using the computer interface. Before the brief push, what was the sum of the forces on the cart? After the brief push, what is the sum of the forces on the cart? What should the acceleration be? (Hint: This question requires no calculation.) 12. Sketch a free body diagram of the cart. Part C Friction 13. Place the friction block flat on your table, and increase the tension by slowly adding mass to the end of the string (running over a pulley) until the block just begins to slide. At this point, the tension in the string is equal to fs,max, the maximum static frictional force. Use this fact to calculate the static coefficient of friction, us. Draw a free body diagram of the block. 14. Now, using the same setup, carefully find the tension in the string that causes the block to slide along the table at constant velocity after a brief push. At this point, the tension in the string is equal to fk, the kinetic frictional force. Use this fact to calculate the kinetic coefficient of friction, uk. Draw a free body diagram of the block. Be sure to include ALL free body diagrams in your report