Name: Friction Lab Goals: 1. Study the relationship between the frictional force and the normal force. Static Frictional Force: In the first part of this lab we will use the weight of a hanging mass to exert a known force on a wooden block. We will adjust this known force to measure the exact force required to overcome the static frictional force acting on a block. We will verify that the maximum static frictional force is proportional to the normal force by varying the normal force acting on the block for each measurement. 1. Use one of the electric scales to measure the mass of the wooden block at your table. Do not place the mass hanger on the scale when measuring the mass of the block. 2. Place the wooden block on the opposite side of the track from the pulley. Hang the mass hanger over the pulley. Orient the block so that the Velcro side is facing down. 3. Adjust the height of the pulley so that the string is parallel with the track. 4. Gradually add mass to the hanger until the weight from the hanger generates enough force to cause the block to begin sliding when starting from rest. 5. Add/remove mass from the hanger until the exact mass required to pull the block is determined to within ± 5 grams. 6. In the table on the last page of the lab, record the normal force acting on the block. 7. Now, record the force exerted by the hanging mass. (Make sure you account for the mass of the hanger itself). 8. Place a 100 gram mass on top of the wooden block to increase the normal force between the block and the track. Now, repeat steps 2-7. 9. Add an additional 100 gram mass to the top of the wooden block. Repeat steps 2-7. 10. Add a third 100 gram mass to the top of the wooden block. Repeat steps 2-7. 11. Use an electric scale to measure the mass of the mass bar. Record this mass on the last page of this lab for reference. Remove the 100 gram masses from the wooden block and place the mass bar on top of the wooden block and repeat steps 2-7.
Static Frictional Force: In the first part of this lab we will measure the coefficient of friction when the wooden block is balanced on its side. 1. Remove all masses from the wooden block and remove all masses from the mass hanger. 2. Rotate the wooden block so that it sits on its side. 3. Repeat steps 2-11 from the previous lab, while keeping the wooden block on its side. Static Frictional Force on a Ram: In this part of the lab, we will determine whether the mass of the block effects the angle at which the block slides down the ramp. 1. Remove the mass bars from the wooden block. Place the wooden block on the opposite side of the track from the pulley. Orient the block so that the Velcro side is facing down. 2. Gradually increase the angle of the ramp until the block begins sliding down the ramp. 3. Using a meter, measure the height of the lifted end of the ramp. 4. The ramp should form the hypotenuse of a right triangle. The hypotenuse is of this triangle is 1.2 meters. Label the height of the ramp in the triangle below. 5. Place the mass bar on top of the wooden block and repeat steps 2-4. Without Mass Bar: With Mass Bar:
Data Analysis: 1. Go to the Honors Physics Assignments page on www.bobsnotes.org and download the Excel file or the Numbers file. Type your data into this file and record the slope of the data below. Wooden Block Laying Flat: Slope = Wooden Block Laying on Its Side: Slope = 2. Calculate the angle at which the wooden block begins to slide down the ramp in the third part of this lab. Without Mass Bars: θ = With Mass Bars: θ =
Questions: 1. In this lab you found the minimum force required to move a wooden block. What physical quantity is this force equivalent to? 2. Does the maximum static frictional force of the wooden block depend on the normal force between the block and the track? Explain how your data can be used to justify your answer. 3. If the Data Analysis portion of this lab, you made a graph of F hanger vs. F N. What are the units of this slope? 4. What physical quantity does the slope of this graph tell you? Explain your reasoning. 5. Does the static coefficient of friction depend how the wooden block was oriented? What data do you have to justify this conclusion? 6. In the final part of this lab you measured the angle at which the wooden block began sliding down a ramp. Did this angle depend on the total mass of the wooden block + mass bar? 7. Briefly explain why the angle would or would not depend on the mass of the wooden block.
Data: Mass Bar: grams F N (N) F hanger (N) F N (N) F hanger (N)