PHYS310 Lab 6 Types of Forces

Experiment 1: Friction


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

2. Assume the mass of the cup and water to be equal to the mass of water alone. Calculate the normal force FN for 300 g and 150 g. Use these values to complete the table above.

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). Calculate and label the force due to gravity mg, the normal force FN, and the friction force Ff. What makes this a state of equilibrium?

5. What is the ratio of the applied force to the normal force F1/FN1? Compare this to your values for F2/FN2. What can you conclude about the ratio between the normal force and the applied force of friction?

6. The ratio Ff/FN is called the coefficient of friction between the two materials in question. We can also write Ff = μFN with the Greek letter μ representing the coefficient of friction. Does it take more force to slide an object across a surface if there is a high value of μ or a low one?

Experiment 2: Velocity and Air Resistance


  1. What are we assuming by using the average velocity from Procedure 1 to estimate the height of the fall in Procedure 2?
  2. Is the object actually traveling at the average speed over the duration of its fall? Where does the acceleration occur?
  3. Draw a free body diagram for a) the coffee filter right as it begins to fall (brief acceleration) and b) once the filter has reached terminal velocity (constant velocity).
  4. 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.
  5. Draw the FBD for the 2-filter combination falling at constant velocity. What is the magnitude of the force of air resistance in this case compared to with only one filter?
  6. How would the FBD differ for a round rubber ball dropped from the same height? How would the acceleration differ over the course of the fall?


PHYS310 Lab 6 Types of Forces
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