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Coefficient of Static Friction Lab Name:______Date:______Mod:______Pre-Lab Questions: 1. Explain the difference between kinetic friction and static friction. 2. What is a coefficient of friction? 3. How is friction produced for both kinetic and static friction? 4. Does the surface area in contact the two surfaces causing the friction influence the friction force? (Example: Large and wide truck tires compared to small and skinny car tires) 5. In the experiment, the string that is attached to the wood block and goes over the pulley should be ______(Blank)______to the surface of the track. 6. In the experiment, do you remove the pennies from the cup before moving on to the next step or leave them in the cup?

Purpose: - To measure the coefficient of static friction for a block of wood on different surfaces using a pulley system and mass.

Materials: - Triple-Beam Balance - Pulley - Wood block w/ other surface - String - Pasco Track - Plastic Cup - Track supports (2) - Large Paper Clip - Pennies (100+)

Procedure: 1. Construct the apparatus as shown below. Pick a flat surface on the track to place the wood block and determine whether the wood side or the other surface is used to be in contact with the track. Use this spot for each trial in the experiment. Make sure the string across the track is parallel to the surface.

a. On the picture, draw and label all the forces acting in the system.

2. After setting up the lab, take the wood block and find its mass using the balance. Record its mass in the data table and place it back onto the track.

3. To overcome the static frictional force, mass must be added to the cup on the end of the string until the wooden block JUST BEGINS TO MOVE AND SLIDE. To do this, add mass to the cup by placing pennies or other kinds of mass into the cup until motion is seen. When placing the pennies in the cup, make sure to do it slowly and not just drop them in.

4. Once the wood block begins to move, take the cup with the pennies and find its mass using the triple-beam balance. Record the mass in the data table.

Coefficient of Static Friction Lab 1 Methacton High School Physics Department 5. Remove the pennies or other masses from the cup to begin the next trail. Next place 15 pennies on the wood block and find its mass using the balance. Record the mass in the data table.

6. Place the wood block back onto the track and add pennies to the cup until the block begins to move again. Then take the cup with the pennies and find its mass using the triple-beam balance, record the mass in the data table.

7. Repeat the experiment for an additional 30, 45 and 60 pennies on the wood block.

8. Once all the data is collected for the total mass of wood block and total mass of cup, calculate the weight of each value and record it in the table.

Data Table: Wood Block Total Mass of Total Weight of Total Mass of Cup Total Weight of Wood Block + Wood Block + + Pennies (g) Cup + Pennies Pennies (g) Pennies (N) (N) Block Block + 15 Pennies Block + 30 Pennies Block + 45 Pennies Block + 60 Pennies

Procedure (continued): 9. Make a graph that shows the relationship between the total weight of the cup and the total weight of the wood block. The graph’s format should look like the diagram below:

10. Plot all the points on the graph and draw a line of best fit if drawing it by hand. If using Excel, make sure to label the title, axes and add a trend line.

Post-Lab Questions:

1. If the weight of the wood block was changes, how would that affect the static friction force? Does the weight of the wood block effect the coefficient of static friction?

2. Explain at least 3 sources of error in the experiment and give an explanation of how to correct for these errors if the experiment were to be repeated.

3. Derive why where is the total mass of the wood block and is the total mass of the cup. Make sure to show all work to earn full credit for this problem.

Coefficient of Static Friction Lab 2 Methacton High School Physics Department

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