Description
Maximum Static Friction.
Total mass
(m) Kg
Normal force
(N)
Trial 1
Peak static friction N
Average
Trial 2
peak static
friction
Trial 3
(N)
0.7
3.46
3.65
3.69
0.9
4.44
4.28
4.75
1
5.15
5.23
4.96
1.2
6.42
6.27
6.38
1.4
7.04
7.15
7.27
1.5
7.68
7.82
7.77
Table Two: Kinetic Friction.
Kinetic friction N
Average
Normal force
Total mass
(m) Kg
(N)
kinetic
Trial 1
Trial 2
Trial 3
friction
(N)
0.7
2.19
2,24
2.18
0.9
2.70
2.67
2.61
1
3.08
3.12
3.17
1.2
3.78
3.7
3.62
1.4
4.29
4.36
4.18
1.5
4.61
4.69
4.72
Data Table 3-A
Data: Block( with no additional mass) 0.50 Kg
Kinetic
Acceleration
friction force
Trial
k
(m/s2)
(N)
1
3.12
2
3.21
3
3.09
Average coefficient of kinetic friction:
Data Table 3-B
Data: Block + 0.70 Kg as additional mass, m total=1.2Kg
Kinetic
Acceleration
friction force
Trial
k
(m/s2)
(N)
1
3.17
2
3.2
3
3.15
Average coefficient of kinetic friction:
Note: In the data table 3-B, you need to add the 0.70 kg to the mass of the block.,
so the total mass will be 1.2 Kg
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
Lab 6 “Investigating Static and Kinetic Frictions.”
Name
Date
Whenever two surfaces that are in contact with each other try to move pass one another there is a force that
resists the motion. In some case you could push on an object trying to move it and the object doesn’t move. The
force of static friction fs balances your force. This is because in order to move an object you need to apply a
force larger or equal to the maximum possible static friction, fsmax .Once moving the object still offers some
resistance and if you stop pushing the object will immediately start to slow down to a stop, the force responsible
for this behavior is the force of kinetic friction, fk.
In this experiment, you will use a Force Sensor to study static friction and kinetic friction on a tray.
Purpose: To find the graphical and mathematical relationship between the forces of maximum static and
kinetic frictions and the normal force on the objects, as to determine the coefficients of static and kinetic
frictions for the surface being studied.
Materials:
•
Computer with Logger Pro;
•
Mass sets;
•
Lab Pro with dual range force sensor;
•
String;
•
Ramp;
•
Trays.
Preliminary questions:
1.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? Explain your answer.
2.How do you think the force of friction is related to the weight of the box? Explain.
3.Create a force or free body diagram for the case when you are pushing on the box without moving it and when
it slides across the floor at a constant velocity.
1
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
Procedure:
Part I Practice Pulling.
1. Measure the mass of the tray 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. Hold the Force Sensor in position as ready to pull the block, but without the string. Click
Force Sensor to zero.
to set the
4. Tie string on the tray to the hook on the Force Sensor. Place a total of 200g 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, increase the
force until the block starts to slide, and then keep the block moving at a constant speed.
5. 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.
6. Copy the force vs. time graph 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.
Part 2 Measuring Maximum Static Friction 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.
7. Remove all masses from the block.
8. Click
to begin collecting data and pull as before to gather force vs. time data.
9. 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.
10. Drag across the 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.
11. Repeat Steps 8-10 for two more measurements and average the results to determine the reliability of your
measurements. Record the values in the data table.
12. Add masses totaling 200 g to the block. Repeat Steps 9 – 12, recording values in the data table.
13. Repeat for additional masses of 400, 600, 800, 1000, and 1200 g. Record values in your data table.
2
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
DATA:
Mass of block
0.50 kg
Table One: Maximum Static Friction.
Total
mass
(m)
Normal
force
(N)
Trial 1
Peak static friction
Trial 2
Trial 3
Average
peak static
friction
(N)
Table Two: Kinetic Friction.
Total
mass
(m)
Normal
force
(N)
Trial 1
Kinetic friction
Trial 2
Trial 3
Average
kinetic
friction
(N)
3
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
Part 3 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 a 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.
Wooden block
Push
Figure 2
15. Place the Motion Detector on the lab table about 2 m from a block of wood, as shown in Figure 2. Use the
same surface you used in Part II. Position the Motion Detector so that it will detect the motion of the block
as it slides toward the detector.
16. Tap Meter. Disconnect the Force Sensor. If your Motion Detector has a
switch, set it to Normal. Connect the Motion Detector to DIG 1 of
LabQuest. Choose New from the File menu. If you have an older sensor
that does not auto-ID, manually set up the sensor.
17. Practice sliding the block toward the Motion Detector by giving the block a very short push, 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
0.15 m for Motion Detectors with a switch or 0.4 m for those without.
18. Collect data for the sliding block.
a. Start data collection.
b. After a moment, give the block a brief push so that it slides toward the Motion Detector.
19. Inspect your graph.
Examine the graph of velocity vs. time.
b. The velocity graph should have a portion with a linearly decreasing section corresponding to the freely
sliding motion of the block. Repeat data collection if needed.
a.
20. Fit a straight line to this portion of the data, the slope of which is the block’s acceleration.
a.
b.
c.
d.
e.
Tap and drag across the region of linear decrease to select the data points.
Choose Curve Fit ►Velocity from the Analyze menu.
Select Linear as the Fit Equation to fit a straight line to the velocity data.
Record the magnitude of the slope of the fitted line, which is the block’s acceleration, in your data table.
Select OK.
21. Repeat Steps 18–20 two more times.
4
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
22. Place masses totaling 500 g on the block. Fasten the masses so they will not separate from the block. Repeat
Steps 18–20 three times for the block with masses. Record acceleration values in your data table.
Data Table 3-A
Data: Block with no additional mass 0.50 Kg
Trial
Acceleration
(m/s2)
Kinetic friction force
(N)
k
1
2
3
Average coefficient of kinetic friction:
Data Table 3-B
Data: Block with 0.70 Kg additional mass
Trial
Acceleration
(m/s2)
Kinetic friction force
(N)
k
1
2
3
Average coefficient of kinetic friction:
Analysis:
Data Table 1 and 2.
1. 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?
2. For Part II, calculate the normal force of the table on the block alone and with each combination of added
masses. Since the block is on a horizontal surface, the normal force will be equal in magnitude and opposite
in direction to the weight of the block and any masses it carries. Fill in the Normal Force entries for both
Part II data tables.
3. Use logger Pro to graph (data table 1)of the average static friction force (vertical axis) vs. the normal force
(horizontal axis). Comment on the relationship and write the corresponding equation. Explain the meaning
of the slope and the y-intercept.
4. Use logger Pro to graph(data table 20 of the average kinetic friction force (vertical axis) vs. the normal force
(horizontal axis). Comment on the relationship and write the corresponding equation. Explain the meaning
of the slope and the y-intercept.
5. Does the force of static friction depend on the weight of the block? Explain.
6.
Does the coefficient of kinetic friction depend on the weight of the block? Explain.
5
Miami Dade College/North Campus
PHY1004L, PHY2053L, and PHY2048L
Data table 3.
1. Your data from Part III also allow 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, determine the coefficient of kinetic friction for each trial and enter the values in the
data table. Also, calculate an average value 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 weight of the block? Explain.
5. Does the coefficient of kinetic friction depend on the weight of the block? Explain
6. Compare your coefficients of kinetic friction determined in Part 3-A to that determined in Part II.. Discuss the
values. Do you expect them to be the same or different?
7. Calculate the percent difference between part 2 and part 3-A.
Show all formulas and calculations when needed.
Write the goal and the conclusion for the lab.
6
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