College Physics I
Lab #7: Conservation of Energy, Work & Friction
Objective:
To study the conservation of energy of an object moving down an incline. To calculate energy lost
due to friction and study the effect of increasing the incline angle on the kinetic friction.
Equipment:
?
?
?
?
?
Carpenteràtape measure
Incline consisting of wooden plank and books for elevation
Your phoneàstopwatch
Flat, smooth object that will slide down the incline, such as a metal jar lid, etc.
Kitchen or bathroom scale
Background & Equations:
y
????
??
?????
??
? = ???
x
????
1
???? + ???? = ???? + ????
1
2
conservation of energy without non-conservative forces,
(eq. 1)
1
?????? + ???????? = 2 ?????? + ????????
1
(eq. 2) conservation of energy equation simplifies to,
???????? = 2 ??????
(eq. 3) if ???? = 0 ??/?? (object starts from rest) and
???? = 0 ?? (object reaches the ground level), then final
velocity can be obtained by,
???? = ?2??????
(eq. 4) giving theoretical, accepted result.
?????? = ??? + ???
work done by non-conservative forces, such as friction is
equal to the change in kinetic energy plus the change in
potential energy (eq. 5).
?? = ??(???)
work is also equal to the force times the displacement (eq.
6).
????,???????????????????????? =
?? = ??????
2???
??
(eq.7), where ??? is the total distance traveled by the object
down the incline in time ??.
friction is equal to the coefficient of friction times the normal
force (eq. 8).
2
Procedure:
1. Measure the mass of your object using a scale. Record in the table below.
2. Sample equipment setup:
????
???
??
????
3. Measure the height of the book(s) and record in the table below (???? ).
3
4. Calculate the incline angle using tan(??) ???? sin (??), The angle should be around 20 degrees for
part 1. You will increase the angle in each part of this lab.
5. Record the length of the incline (???? ). Hold the object at the top of the incline and record its
position (???? ).
????
???
????
6. Let the object go from its initial position, without pushing (just let it slide), and at the same time
start the stopwatch. Stop the stopwatch once the object reaches the bottom of incline. Record the
time in the table below.
7. Repeat this procedure four times, increasing the angle each time.
8. Perform all calculations within the data table. Discuss your results.
4
Note: Release the ball from the same initial position for all trials within one part. Use the
same object for all parts.
Part 1: Set ???? to about 20 degrees.
Data table 1a:
m (kg):
??1 (degrees):
???? (m):
??? = ???? ? ???? (m):
Data table 1b:
Trial #
??? (m)
t (s)
–
–
????,???????????????????????? ????,?????????????????????
(m/s)
(m/s)
????
(J)
????,??????.
(J)
????,??????.
(J)
%
error
1
2
3
Average:
–
–
–
Assume % error comes from friction. Calculate energy lost due to friction and the force of friction
(eq. 5 &6). Using the free body diagram on the first page, calculate the normal force.
Data table 1c:
?????????????????? (J):
Friction (N):
Normal Force (N):
Part 2: Set ???? to about 45 degrees.
Data table 2a:
m (kg):
??2 (degrees):
???? (m):
??? = ???? ? ???? (m):
5
Data table 2b:
Trial #
??? (m)
t (s)
–
–
????,???????????????????????? ????,?????????????????????
(m/s)
(m/s)
????
(J)
????,??????.
(J)
????,??????.
(J)
%
error
1
2
3
Average:
–
–
–
Assume % error comes from friction. Calculate energy lost due to friction and the force of friction
(eq. 5 &6). Using the free body diagram on the first page, calculate the normal force.
Data table 2c:
?????????????????? (J):
Friction (N):
Normal Force (N):
Part 3: Set ???? to about 60 degrees.
Data table 3a:
m (kg):
??3 (degrees):
???? (m):
??? = ???? ? ???? (m):
Data table 3b:
Trial #
??? (m)
t (s)
????,???????????????????????? ????,?????????????????????
(m/s)
(m/s)
????
(J)
????,??????.
(J)
????,??????.
(J)
%
error
1
2
6
3
Average:
–
–
–
–
–
Assume % error comes from friction. Calculate energy lost due to friction and the force of friction
(eq. 5 &6). Using the free body diagram on the first page, calculate the normal force.
Data table 3c:
?????????????????? (J):
Friction (N):
Normal Force (N):
Part 4: Set ???? to about 80 degrees.
Data table 4a:
m (kg):
??4 (degrees):
???? (m):
??? = ???? ? ???? (m):
Data table 4b:
Trial #
??? (m)
t (s)
–
–
????,???????????????????????? ????,?????????????????????
(m/s)
(m/s)
????
(J)
????,??????.
(J)
????,??????.
(J)
%
error
1
2
3
Average:
–
–
–
Assume % error comes from friction. Calculate energy lost due to friction and the force of friction
(eq. 5 &6). Using the free body diagram on the first page, calculate the normal force.
7
Data table 4c:
?????????????????? (J):
Friction (N):
Normal Force (N):
Lastly, make a graph in excel of friction vs. normal force using data points from data tables: 1c,
2c, 3c, and 4c. The graph will contain 4 points only. It should be a scatter plot with a linear best
fit trendline going through the points. Look at the background equations, the free body diagram,
and the graph. Discuss the results.
8
Lab Report Guidelines
Laboratory reports should be individual.
Laboratory reports should consist of the following:
1. Cover Sheet:
a. Your name
b. Experiment name and lab number
c. Date
d. Laboratory partners.ames (if working in a group)
2. Scans or pictures of your completed data tables from the lab manual.
3. Calculations, including percent errors. Use the formula below to find percent errors
between accepted and experimental measurements:
Theoretical value = accepted value, predicted value
Experimental value = measured value or calculated from the experimental measurements
4. Graphs (if any required by the experiment):
a. Completed in excel
b. Make sure you have the axes labeled and the slope equation displayed on chart
5. Discussion of results:
a. This is the most important part of your lab report as this is where you analyze
your data
b. Explain the basic idea of the experiment and discuss your measurements, results,
your observations, analyze the graphs (if any required by the experiment)
c. Describe how your experimental results agree with the theory and discuss percent
errors and their possible source
6. Conclusion:
a. Revisit the theory and briefly talk about your results
b. Discuss the significance of the experiment/state what you¥ learned from the
experiment
If possible, please combine pages of your laboratory reports into single PDF before
submitting to Canvas.

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