15200 PHYS Mechanics
IUPUI Physics Department
Lab 04: Friction
OBJECTIVE
In this experiment you will be verifying the relationship between the force of friction acting on a
sliding object and its weight. You will also be measuring the coefficients of static and kinetic
friction.
This experiment is adapted from Vernier Physics with Computers experiments using Logger Pro.
EQUIPMENT
computer
Vernier computer interface
Logger Pro
Vernier Motion Detector
Vernier Force Sensor
string
block of wood with hook
electronic balance
set of standard masses
PROCEDURE
PART I STARTING FRICTION
1. Measure the mass of the block and record it in the data table.
2. Connect the Dual-Range Force Sensor to Channel 1 of the interface. Set the range switch on
the Force Sensor to 50 N.
3. Open the file 12a Static Kinetic Frict from the Physics with Computers folder.
4. Tie one end of a string to the hook on the Force Sensor and the other end to the hook on the
wooden block. Place a total of 1 kg mass on top of the block, fastened so the masses cannot
shift. Practice pulling the block and masses with the Force Sensor using this straight-line
motion: Slowly and gently pull horizontally with a small force. Very gradually, taking one
full second, increase the force until the block starts to slide, and then keep the block moving
at a constant speed for another second.
5. Sketch a graph of force vs. time for the force you felt on your hand. 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. (Graph paper is printed on your
worksheet.)
6. Hold the Force Sensor in position, ready to pull the block, but with no tension in the string.
Click
to set the Force Sensor to zero.
7. Click
to begin collecting data. Pull the block as before, taking care to increase the
force gradually. Repeat the process as needed until you have a graph that reflects the desired
motion, including pulling the block at constant speed once it begins moving. Print or copy
the graph for use in the Analysis portion of this activity.
Lab04: Friction
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PHYS 15200 Mechanics
IUPUI Physics Department
PART II PEAK STATIC AND KINETIC FRICTION
In this section, you will measure the peak static friction force and the kinetic friction force as
a function of the normal force on the block. In each run, you will pull the block as before, but
by changing the masses on the block, you will vary the normal force on the block.
Figure 1
8. Remove all masses from the block.
9. Click
to begin collecting data and pull as before to gather force vs. time data.
10. Examine the data by clicking the Statistics button, . The maximum value of the force
occurs when the block started to slide. Read this value of the maximum force of static friction
from the floating box and record the number in your data table.
11. Drag the across region of the graph corresponding to the block moving at constant velocity.
Click on the Statistics button again and read the average (or mean) force during the time
interval. This force is the magnitude of the kinetic frictional force.
12. Repeat Steps 9-11 for two more measurements and average the results to determine the
reliability of your measurements. Record the values in the data table.
13. Add masses totaling 250 g to the block. Repeat Steps 9 12, recording values in the data
table.
14. Repeat for additional masses of 500, 750, and 1000 g. Record values in your data table.
PART III KINETIC FRICTION AGAIN
In this section, you will measure the coefficient of kinetic friction a second way and compare
it to the measurement in Part II. Using the Motion Detector, you can measure the acceleration
of the block as it slides to a stop. This acceleration can be determined from the velocity vs.
time graph. While sliding, the only force acting on the block in the horizontal direction is that
of friction. From the mass of the block and its acceleration, you can find the frictional force
and finally, the coefficient of kinetic friction.
Figure 2
Lab04: Friction
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PHYS 15200 Mechanics
IUPUI Physics Department
15. Connect the Motion Detector to DIG/SONIC 1 of the Vernier computer interface. Open the
12b Static Kinetic Frict in the Physics with Computers folder.
16. Place the Motion Detector on the lab table 2 3 m from a block of wood, as shown in
Figure 2. Position the Motion Detector so that it will detect the motion of the block as it
slides toward the detector.
17. Practice sliding the block toward the Motion Detector so that the block leaves your hand and
slides to a stop. Minimize the rotation of the block. After it leaves your hand, the block
should slide about 1 m before it stops and it must not come any closer to the Motion Detector
than 0.4 m.
18. Click
to start collecting data and give the block a push so that it slides toward the
Motion Detector. The velocity graph should have a portion with a linearly decreasing section
corresponding to the freely sliding motion of the block. Repeat if needed.
19. Select a region of the velocity vs. time graph that shows the decreasing speed of the block.
Choose the linear section. The slope of this section of the velocity graph is the acceleration.
Drag the mouse over this section and determine the slope by clicking the Linear Fit button,
. Record this value of acceleration in your data table.
20. Repeat Steps 18-19 four more times.
21. Place masses totaling 500 g on the block. Fasten the masses so they will not move. Repeat
Steps 18-19 five times for the block with masses. Record acceleration values in your data
table.
Each student is required to turn in a completed worksheet by the end of the lab
session unless otherwise indicated by the lab instructor.
Lab04: Friction
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