FRICTION LABS
NAME ______________________________________ PERIOD_______ DATE_______________
PART I: DOES SURFACE AREA AFFECT FRICTION?
Friction may be defined as the resistance to motion caused by one surface rubbing against another.
The frictional force acts in a direction opposite to that of the motion. Frictional forces are sometimes
necessary. However many times machines lose some of their input energy to friction. This loss
reduces the efficiency of the machine. Typically this “loss” of energy is actually just a conversion to
heat energy and sometimes sound energy.
I.
Purpose:
a. Determine what factors affect friction
b. Measure the effect of changing surfaces on friction
c. Measure the difference between sliding and rolling friction
d. Calculate the coefficient of friction
II.
Procedure:
a. Measure the areas of the three sides of your block (cm), then enter it in the data table
below.
Largest Side (cm2)
Middle Face (cm2)
Smallest Face (cm2)
Length x Height =
Length x Height =
Length x Height =
b. Attach a spring scale to your wood block. *(5 N scale would work best, as the block
without any masses added to it does not need much force to achieve a constant
velocity).
c. Place the block on its largest area face.
d. Begin pulling the spring scale until you get a relatively constant force to move the block.
e. Record this force in the data table and repeat step “d” three more times recording your
results.
f. Calculate the average spring scale reading.
g. Repeat all steps, this time using the middle area face.
h. Repeat all steps, this time using the smallest area face.
Surface Area
Force Trial #1
Force Trial #2
Force Trial #3
Average Force
III.
Largest Face
Middle Face
Smallest Face
Analysis
a. Compare the surface areas of your largest face and smallest face.
How many times larger is your largest surface area than your smallest surface area?
Complete the table below:
LARGEST FACE (cm2)
SMALLEST FACE (cm2)
TIMES LARGER
( Large Face /Small Face)
SURFACE
AREAS
b. Surface area can be considered to affect friction if an increase in the surface area
results in a corresponding increase of the frictional force.
i. *Ex: If the surface area doubles, then the frictional force doubles. If this does
not occur then surface area does not affect friction.
1. Look at your results, decide and write your answer below:
a. *Does surface area affect friction?
PART II: DOES MASS AFFECT THE FRICTIONAL FORCE?
You will use your block on its largest face and move it along your desktop/countertop.
1. Weigh your block on a triple beam balance and record here: _______________g
a. You will need this mass to add to your data tables throughout the lab!!
2. Set up your block on its largest face.
3. Use a spring scale (10N scale would be best) to determine the force necessary to pull the block
at a constant velocity.
a. Record your data
b. Repeat twice more and record your data
i. Determine the average force necessary to move the block at a constant velocity.
1. Record your answer in the data table.
4. Place a 500 g mass on top of your block and pull the block at a constant velocity.
a. Record your data
b. Repeat twice more and record your data
i. Determine the average force necessary to move the block at a constant velocity.
1. Record your answer in the data table.
5. Repeat step #3 with a 1000 g mass.
6. Repeat step #3 with a 1500 g mass.
BLOCK
BLOCK + 500g
BLOCK +
1000g
BLOCK +
1500g
Mass of Block and
Masses (g):
Force Trial #1
Force Trial #2
Force Trial #3
Average Force (N)
7. Analysis
a. As the mass of your block got progressively heavier, did you find a corresponding
increase in the average force required to overcome friction?
b. Why does this occur? Explain.
i. Use this diagram and the forces illustrated by it in your answer.
c. GRAPHING: Plot the average force to overcome friction for the 4 measured values.
Place mass on the x axis and average force on the y axis. Make a best fit line and
calculate the slope value. Show all work and final answer in N/g on your graph.
PART III: DOES THE SURFACE AFFECT THE FRICTIONAL FORCE?
Repeat the procedures for part three. However, this time do all of your measurements on a piece of
carpet rather than the desk top or counter top. Record your results below:
BLOCK
BLOCK + 500g
BLOCK +
1000g
BLOCK +
1500g
Mass of Block and
Masses (g):
Force Trial #1
Force Trial #2
Force Trial #3
Average Force
1. Analysis
a. Does the surface appear to affect the frictional force?
b. Why are lubricants, such as oil in a car’s engine, used when surfaces are in contact?
c. GRAPHING: Plot the average force to overcome friction for the 4 measured values.
Place mass on the x axis and average force on the y axis. Make a best fit line and
calculate the slope value. Show all work and final answer in N/g on your graph.
*Color-code your graphs to distinguish them.
PART IV: HOW IS SLIDING FRICTION DIFFERENT FROM ROLLING FRICTION?
1.
2.
3.
4.
Place your block on its largest face.
Record the force needed to move it at a constant velocity.
Repeat using a 500g, 1000g, and 1500g masses.
Record your results in the table below.
BLOCK
BLOCK + 500g
BLOCK + 1000g
BLOCK + 1500g
Mass of Block
and Masses
(g):
Sliding Force
Rolling Force
5. Repeat the above experiment. However, this time place pencils as rollers beneath your block
face, then record the force using the spring scales as above.
6. Record results in the table above.
7. Analysis
a. Does the presence of a rolling device appear to change the effort required to overcome
friction? Explain.
b. Why are ball bearing used in wheels? *(Research this on your own!)
c. GRAPHING: Plot the average force to overcome friction for the 4 measured values.
Place mass on the x axis and average force on the y axis. Make a best fit line and
calculate the slope value. Show all work and final answer in N/g on your graph. *
Color-code to distinguish “sliding friction” and “rolling friction”.
PART V: HOW CAN I CALCULATE THE COEFFICIENT OF FRICTION?
As you have discovered, different surfaces will require different forces to overcome friction (desk top
vs. carpet ). The ratio of the force required to overcome friction (Fp) compared to the weight of the
object (Fwt)is called the Coefficient of Friction. The formula for calculating the coefficient of friction
is then :
p/Fwt
It is a decimal value, less than one and is a constant for any two surfaces in contact.
In this activity you will calculate the coefficient of friction for your wood block on the desk top and
then the wood block on the floor.
Procedure: DESK TOP
1. Find the mass of your wood block and record in the table below.
a. Mass of wood block: _______________g
i. Convert to kg: ______________kg
1. Multiply by the gravity of the Earth (9.8m/s2): _______________N
a. THIS IS YOUR Weight Force (Fwt) for the “BLOCK” column of your
data table.
2. Measure the force necessary to pull your block on the desk top and record. After three trials,
calculate the average pull force (Fp) and record.
3. Calculate the Coefficient of Friction and record.
4. Add a 500g mass to your block.
a. Convert to kg: ______________kg
i. Multiply by the gravity of the Earth (9.8m/s2): _______________N
1. THIS IS YOUR Weight Force (Fwt) for the “BLOCK + 500g” column of your
data table.
ii. Repeat steps 2 and 3 for this column.
5. Add a 1000g mass to your block.
a. Convert to kg: ______________kg
i. Multiply by the gravity of the Earth (9.8m/s2): _______________N
1. THIS IS YOUR Weight Force (Fwt) for the “BLOCK + 1000g” column of your
data table.
ii. Repeat steps 2 and 3 for this column.
6. Add a 1500g mass to your block.
a. Convert to kg: ______________kg
i. Multiply by the gravity of the Earth (9.8m/s2): _______________N
1. THIS IS YOUR Weight Force (Fwt) for the “BLOCK + 1500g” column of your
data table.
ii. Repeat steps 2 and 3 for this column.
7. Add a 2000g mass to your block.
a. Convert to kg: ______________kg
i. Multiply by the gravity of the Earth (9.8m/s2): _______________N
1. THIS IS YOUR Weight Force (Fwt) for the “BLOCK + 2000g” column of your
data table.
8. Repeat the above directions for the FLOOR data table below (next page).
DESK TOP
BLOCK
BLOCK + 500g
BLOCK +
1000g
BLOCK +
1500g
BLOCK +
2000g
BLOCK
BLOCK + 500g
BLOCK +
1000g
BLOCK +
1500g
BLOCK +
2000g
Mass of Block
and Masses
(g):
Force of
Weight (Fwt)
Force Trial #1
Force Trial #2
Force Trial #3
Average Force
of Pull (Fp)
Coefficient of
Friction:
p/Fwt
FLOOR
Mass of Block
and Masses
(g):
Force of
Weight (Fwt)
Force of Pull
(Fp) Trial #1
Force of Pull
(Fp) Trial #2
Force of Pull
(Fp) Trial #3
Average Force
of Pull (Fp)
Coefficient of
Friction:
p/Fwt
Analysis:
a. How does the slope of the two lines compare to the surfaces tested?
b. What does this tell you about the frictional force on the floor compared to the desktop?
c. Why might this be so?
d. Describe how the Coefficient of Friction may have changed during the course of the
experiment. Did it change drastically? Why? Explain. (Use the Fp and Fwt in your
explanation).
e. GRAPHING: Plot the average force to overcome friction for the 5 measured values.
Place mass on the x axis and average force on the y axis. Make a best fit line and
calculate the slope value. Show all work and final answer in N/g on your graph. *
Color-code to distinguish “Desk Top Friction” and “Floor Friction”.
f. GRAPHING (Coefficient of Friction): Make a new graph plotting the Force of Weight
(Fwt) on the X Axis and Force of Pull (Fp) on the Y Axis. Make a best fit line. *Colorcode to distinguish the Coefficient of Friction for “desktop” and “floor”.
i. How do the lines in your first graph (step “e”) compare to the lines in your
second graph (step “f”)? Explain why this is the case.
GRAPHING SUMMARY:
GRAPHING SUMMARY
HAND
GRAPH
NO
EXCEL
GRAPH
NO
COMMENTS
PART II:
DOES MASS AFFECT THE FRICTIONAL FORCE?
YES
YES
COMBINE TOGETHER WITH
PART III
PART III:
DOES THE SURFACE AFFECT THE FRICTIONAL FORCE?
YES
YES
COMBINE TOGETHER WITH
PART II
PART IV:
HOW IS SLIDING FRICTION DIFFERENT FROM ROLLING
FRICTION?
YES
YES
PART V:
HOW CAN I CALUCLATE THE COEFFICIENT OF
FRICTION?
YES
YES
PART I:
DOES SURFACE AREA AFFECT FRICTION?
FRICTION LABS CONCLUSION SHEET:
NAME ______________________________________ PERIOD_______ DATE_______________
*DIRECTIONS: TYPE YOUR ANSWERS TO EACH OF THE FOLLOWING QUESTIONS AND ATTACH TO THE
BACK OF YOUR COMPLETED LAB.
DOES SURFACE AREA AFFECT FRICTION?
c. Surface area can be considered to affect friction if an increase in the surface area
results in a corresponding increase of the frictional force.
i. *Ex: If the surface area doubles, then the frictional force doubles. If this does
not occur then surface area does not affect friction.
1. Look at your results and decide: *Does surface area affect friction? How do you know?
Explain.
DOES MASS AFFECT THE FRICTIONAL FORCE?
2. As the mass of your block got progressively heavier, did you find a corresponding increase
in the average force required to overcome friction?
3. Why does this occur? Explain.
ii. Use this diagram and the forces illustrated by it in your answer.
DOES THE SURFACE AFFECT THE FRICTIONAL FORCE?
4. Does the surface appear to affect the frictional force?
5. Why are lubricants, such as oil in a car’s engine, used when surfaces are in contact?
HOW IS SLIDING FRICTION DIFFERENT FROM ROLLING FRICTION?
6. Does the presence of a rolling device appear to change the effort required to overcome
friction? Explain.
7. Why are ball bearing used in wheels? *(Research this on your own!)
HOW CAN I CALUCLATE THE COEFFICIENT OF FRICTION?
8. How does the slope of the two lines compare to the surfaces tested?
9. What does this tell you about the frictional force on the floor compared to the desktop?
10. Why might this be so?
11. Describe how the Coefficient of Friction may have changed during the course of the
experiment.
12. How do the lines in your first graph (step “e”) compare to the lines in your second graph
(step “f”)? Explain why this is the case.