Lab: Types of Forces

Experiment 1: Friction

Questions:

1. What happened to your applied force F_app 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 (F_N) for 300 g, 150 g, and 100 g. Use these values to compute the ratio of the Applied Force (F_app) to the Normal Force (F_n).

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?

F_N= mg
F_{N (300 g)} = _________kg × 9.8 m/s² = ___________
F_{N (150 g)} = _________kg × 9.8 m/s² = ___________
F_{N (100 g)} = _________kg × 9.8 m/s² = ___________

3. Why doesn't the normal force F_N 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 F_f, 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

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?