In this experiment, students determine the coefficients of static and kinetic friction and derive the equations for static and kinetic friction.

• Microsoft Word version of this lab:
  
  • frictionGLX_docs.zip (1.5 MB)

• Xplorer GLX (PS-2002)
• Motion Sensor (PS-2103)
• Force Sensor (PS-2104)
• Discover Friction Accessory (ME-8574)
• Ohaus Triple-Beam Balance (SE-8723)
• 250 g or 500 g Masses from Dynamics Systems
• Braided Physics String (SE-8050)

1. Using a balance, determine the mass of the Friction Tray. Place a 250 g mass in the Friction Tray. Find the combined mass of the Friction Tray with the 250 g mass. Enter the value into the Data Table below.
2. Calculate the Normal Force of the Friction Tray with the mass. Enter the value into the Data Table below.
3. Set up the equipment as in the picture above with the rear of the friction tray approximately 15 cm from the Motion Sensor.
4. Press the button on the GLX.
5. Gently pull the Force Sensor, dragging the friction tray away from the Motion Sensor.
6. Observe the graphs. When the velocity remains fairly constant, press the button.
7. Press and select the Smart Tool. (If the Smart Tool is only available on the Velocity-Time graph, select "Toggle Active Area" first.) Use the Smart Tool to find the maximum static frictional force. Enter this value into the Data Table.
8. Press and select the Statistics Tool. Select the area in the Force-Time graph in which the Friction Tray experiences constant velocity. Enter the average value of the force for this region into the Data Table.
9. Repeat the previous steps with the addition of another mass until the data table is completed.

Data Table 1: Maximum Static Friction

Mass (kg)	FN Normal Force (N)	Fs Max. Static Friction (N)	Fk Kinetic Friction (N)

1. Plot and label a graph with Normal Force on the horizontal axis and Static Friction on the vertical axis.
2. Plot and label a graph with Normal Force on the horizontal axis and Kinetic Friction on the vertical axis.

1. Sketch or print-out the Force-Time graph.
   Label the following regions on the Force-Time graph:
   1. A force is being applied and the mass is NOT moving.
   2. A force is being applied just before the mass moves.
   3. A force is being applied and the mass accelerates.
   4. A force is being applied and the mass moves with a non-zero constant velocity.
2. Draw labeled force diagrams for each of the regions mentioned above. Make sure to draw the vectors in the force diagrams with lengths relative to their values. For example, if one force is twice the value of another, its vector should be twice as long.
3. What does the slope of the Static Friction versus Normal Force graph represent physically?
4. Write a y=mx+b equation for the Static Friction graph with the appropriate variables and units.
5. What does the slope of the Kinetic Friction versus Normal Force graph represent physically?
6. Write a y=mx+b equation for the Kinetic Friction graph with the appropriate variables and units.

1. Repeat the experiment with a different Friction Tray.
2. Relate and explain the differences in the slopes of the Static Friction and Kinetic Friction graphs to the type of surfaces beneath each Friction Tray.