Name
Date
(Lab Partner)
Lab 7: Kinetic and Static Friction
Introduction
Insert your introduction here. Write a few lines describing the goals of the lab and basic
principles. Include any important equations that you will use.
Preliminary questions
Q1. In pushing a heavy box across the floor, is the force you need to apply to start the
box moving greater than, less than, or the same as the force needed to keep the box
moving? On what are you basing your choice?
Q2. How do you think the force of friction is related to the weight of the box? Explain.
Part I
Mass of block=__________kg
Include a sketch of force vs. time based on what you felt when you pulled on the block.
Analysis Part I
1. Print out the force vs. time graph drawn in Part I (stored as Run 1). Label the portion
of the graph corresponding to the block at rest, the time when the block just started to
move, and the time when the block was moving at constant speed.
2. Still using the force vs. time graph you created in Part I, compare the force necessary
to keep the block sliding to the force necessary to start the slide. How does your
answer compare to your answer to question 1 in the Preliminary Questions section?
3. The coefficient of friction is a constant that relates the normal force between two
objects (blocks and table) and the force of friction. Based on your graph (Run 1) from
Part I, would you expect the coefficient of static friction to be greater than, less than,
or the same as the coefficient of kinetic friction?
Part II
Tables Part II
Insert tables 1 and 2 here. You can get templates from the course website.
Graphs Part II
Insert graphs of static frictional force vs. normal force and kinetic frictional force vs.
normal force. You may put both sets of data on the same graph. Be sure that each graph
has a label, that the axes are labeled (including units), and display the equation of the
trendline on the graph. Also include results from regression.
Part III
Tables Part III
Insert tables 3 and 4 here. You can get templates from the course website.
Analysis Part III
1. Your data from Part III allows you to determine k. Draw a free-body diagram for the
sliding block. The kinetic friction force can be determined from Newton’s second
law, or F = ma. From the mass and acceleration, find the friction force for each trial,
and enter it in the data table.
2. From the friction force and the normal force, determine the coefficient of kinetic
friction for each trial and enter the values in the data table. Also, calculate an average
value and standard deviation for the coefficient of kinetic friction for the block and
for the block with added mass.
3. Does the coefficient of kinetic friction depend on speed? Explain, using your
experimental data.
4. Does the force of kinetic friction depend on the total weight of the block and
additional mass? Explain.
5. Does the coefficient of kinetic friction depend on the weight of the block?
6. Compare your coefficients of kinetic friction determined in Part III to that determined
in Part II. Discuss the values. Do you expect them to be the same or different?
Conclusion
Write a few concluding remarks. Describe any inconsistencies between results and
expectations. What are the sources of uncertainties?
Sample Calculations
Insert any sample calculations here. These may be added by hand.