# · To conduct your laboratory exercises, use the Laboratory Manual that is available in the classroom. Laboratory exercises on your CD may not be updated.

## Experiment 1: Friction

Table 1: Applied Force Required to Slide Cup

 Cup Material Force Applied F1 m1 = 300 g water Force Applied F2 m2 = 150 g water F1 / FN1 F2 / FN2 Plastic Avg: Avg: Avg: Avg: Styrofoam Avg: Avg: Avg: Avg: Paper F1 m1 = 150 g water F2 m1 = 100 g water F1 / FN1 F2 / FN2 Avg: Avg: Avg: Avg: Surface Description

## Questions:

1. What happened to your applied force Fapp as you decreased the amount of water in the cup?

2.  Assume the mass to be exactly equal to the mass of water. Calculate the normal force (FN) for 300 g, 150 g, and 100 g. Use these values to compute the ratio of the Applied Force (Fapp) to the Normal Force (Fn). Place these values in the rightmost column of Table 1.

What do these last two columns represent? What is the ratio of the normal forces F1 / F300? Compare this to your values for F2/ F150, and F3/F100. What can you conclude about the ratio between the Force Normal and the Force Friction?

FN= mg FN (300 g) = _________kg × 9.8 m/s2 = ___________ FN (150 g) = _________kg × 9.8 m/s2 = ___________ FN (100 g) = _________kg × 9.8 m/s2 = ___________

3. Why doesn’t the normal force FN depend on the cup material?

4. Right as the cup begins to slide the applied force is equal to the force of friction—draw a free body diagram for each type of cup (a total of three diagrams). Label the force due to gravity mg, the normal force FN, and the friction force Ff, but don’t use any specific numbers. What makes this a state of equilibrium?

5. Does it take more force to slide an object across a surface if there is a high value of μ or a low one? Explain your answer

## Experiment 2: Velocity and Air-Resistance

Table 2: Coffee Filter Data

 Procedure 1 1 Coffee Filter 2 Coffee Filters Height of Table (m) Total Time (s) – Trial 1 Total Time (s) – Trial 2 Total Time (s) – Trial 3 Total Time (s) – Trial 4 Total Time (s) – Trial 5 Calculated Average Speed (m/s) Procedure 2 Measured Height (m) Total Time (s) – Trial 1 Total Time (s) – Trial 2 Total Time (s) – Trial 3 Total Time (s) – Trial 4 Total Time (s) – Trial 5 Average Time (s) Calculated Height (m)

## Questions:

1. Draw a FBD for the falling coffee filter. What is the net force?

2. What are we assuming by using the average velocity from Procedure 1 to estimate the height of the fall in Procedure 2?

3. Is the object actually traveling at the average speed over the duration of its fall? Where does the acceleration occur?

4. Draw the FBD for the 2-filter combination, assuming constant velocity. What is the net force?

5. How do your measured and calculated values for the height in Procedure 2 compare? If they are significantly different, explain what you think caused the difference.

6. Why do two coffee filters reach a higher velocity in free fall than one coffee filter?

7. How would the FBD differ for a round rubber ball dropped from the same height?