Measuring the Coefficient of Friction
Objective
The purpose of this lab is to experimentally determine the coefficient of static friction and the
coefficient of kinetic friction for a combination of different materials. The results will be a table
we can then use to understand frictional forces as we study Newton’s Laws of Motion.
Background
The coefficient of friction is a ratio that is calculated by dividing the force to overcome friction
by the weight of an object. When an object is at rest, there is a cohesive force, like the object is
glued to the surface. It takes extra force to break this bond and start and object moving. This
frictional force is called “static friction.” Once an object is moving, it requires less force to
maintain a constant speed. The frictional force of a moving object is called “kinetic friction.”
Kinetic friction is usually less than static friction because it usually takes less force to keep an
object moving once it starts moving.
Materials
 LabQuest Handheld computer
 Dual-Range Force Sensor
 Variety of objects whose coefficient of friction you will determine (one must be a shoe)
 Variety of surfaces to test (you can use the table top, floor, cardboard, Styrofoam,
plywood, tile board, shop apron, Formica countertop, cafeteria tray, etc.)
Procedure:
1. Turn on your LabQuest and plug the Dual-Range Force Sensor into Channel 1 on the top
of the device. When you use the sensor, you will need to zero out the sensor when you
change the orientation. To do that, hold the sensor so the hook is pointing down and
click “Sensor” then “Zero” on the menu bar.
2. Choose the first object to test. Note the surface material of the object. Using the hook on
the sensor, hang the object directly down and find the object’s weight in Newtons. Log
this information in your lab notebook.
3. Choose a test surface. Note in your lab notebook the object and the surface. Place your
force sensor horizontally on the table and re-zero it.
4. Place the object on the surface to be tested. Press the start button on the LabQuest and
slowly start to pull horizontally on the object using the sensor. You will see data being
graphed as you pull. Read the maximum force of static friction between the object and
the surface. On the screen, you will see a spike in the data. The top of the spike is the
Fs,max. You can select it on the screen and the LabQuest will show you the value.
5. Continue pulling the object horizontally at a constant speed. Focus on the object and not
the screen. The force on the screen should be horizontal. To find the average value,
select the starting point of the constant force and drag the pointer to the right to the end of
the constant force data. Select “Analyze” then “Statistics” and then “Force.” The values
will be on the right side of the screen. Record the mean (average) force under Fk,max.
6. Determine the coefficient of static friction (μs) and coefficient of kinetic friction (μk) by
dividing the pulling force by the weight. Record these figures in your data table.
7. Use the same object on at least five different surfaces and repeat the experiment.
8. Repeat the procedure again for a total of three different objects.
As you collect your data, you should have the following columns for each item tested:
Data Table
Object Tested & Material
Weight
Surface Tested
Static Force Kinetic Force
Analysis
After you have created a table of data on a least three different objects, you will need to
calculate the coefficient of friction between the two different materials. Create a table in your
lab notebook with the coefficient of static and kinetic friction. You should have at least 15 rows
of results in your table.
Results - Coefficients of Friction
Material
μ Static
Surface
μ Kinetic
Questions
1. Which materials and surfaces surprised you by being more slippery or more sticky than
you expected?
2. Explain why the coefficient of static friction is greater than the coefficient of kinetic
friction?
3. Why must you pull the object under test at a constant speed? What happens if you don’t?
4. What additional surface/material combinations would you like to test for their coefficient
of friction?
5. What could you have done in this lab to improve the accuracy of your results?
6. What should be done to improve this lab for next year’s students?
Lab Report Checklist:
 Headers are filled in completely
 Introduction
 Material & Procedure
 Data & Observations
 Analysis
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Conclusion
Report is neat, spelling is correct
Units are included where
Signed on the last page