PHYS 205
SPR 2007
LoggerPro Video Analysis – Conservation of Mechanical Energy
You will use Vernier’s LoggerPro video analysis software (http://www.vernier.com/soft/lp.html)
to examine energy conservation in a bouncing mini-basketball. Data for the ball’s position and
velocity will be collected and analyzed as before, but new calculations will be made in order to
obtain the ball’s kinetic, potential, and total energies as it rises and falls after bouncing several
times.
Procedure:
1. Go to the web site http://www.science.tamu.edu/CMSE/videoanalysis/index.asp.
Right click the “Conservation of Energy I (bouncing ball)” “Video Download” link to
download the video “balldropbounce4X” and save it in “My Documents” or on the
desktop.
2. Use LoggerPro to mark the location of the ball in all 78 frames after release as
it rises and falls through four bounces.
3. It is best to turn off the “Toggle Trails”
until the entire movie is marked.
4. In this case, it is advantageous to locate
the origin at the lowest placed marked in the
movie and let “up” be the positive y-direction.
5. Use the meter stick to scale the movie.
6. Once the movie is marked, scale set, and
origin moved to the lowest place marked,
copy and paste the marked movie in the
text box to the right.
7. Make a graph of “Position vs Time” for the vertical motion. Label the graph appropriately.
Highlight and determine the equation of each of the four “sections” of this graph.
8. You may need to change the font size of the equation boxes for better display.
9. Paste the completed graph in this document. Resize as necessary.
QUESTIONS:





What is the mathematical shape of each section?
What does this shape tell us about the motion of the ball?
Describe changes in the sizes of each consecutive section.
What is indicated by the “peak” in each graph section?
What was the acceleration of the ball…
…after release?
_______
…after the first bounce?
_______
…after the second bounce?
_______
…after the third bounce?
_______
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PHYS 205
SPR 2007
10. Select “Insert” and “Graph” from the main toolbar. A new graph appears.
11. Change this new graph to display the “Velocity vs Time” graph of the vertical motion.
Label the graph appropriately. Highlight and determine the equation of each “section” of
this graph.
12. Paste the completed graph in this document. Resize as necessary.
QUESTIONS:







What is the ball doing when the velocity graph has the large “gaps” in it?
What happens to the size of each consecutive gap?
Compare the slopes of each graph section.
What is the ball doing when the velocity of the ball is positive?
What is the ball doing when the velocity of the ball is negative?
What is indicated by these graph sections crossing the x-axis?
What was the acceleration of the ball…
…while falling after release?
_______
…on its way up after the first bounce?
_______
…on its way down after the first bounce?
_______
…on its way up after the second bounce?
_______
…on its way down after the second bounce?
_______
13. You will now make graphs of “Energy vs Time,” but you must first calculate the ball’s
kinetic energy and gravitational potential energy in order to determine its total energy.
14. Select “Data” and “New Calculated Column” from the top toolbar. Name this column
“Gravitational Potential Energy” (PE for short) and give it units of “Joules.”
15. Its equation will be mgh, where m = the mass of the ball = 0.305 kg, h is the vertical
distance, and g = 9.8 m/s/s. You will enter 0.305*9.8*(variable Y) as the equation.
16. To enter the kinetic energy, again select “Data” and “New Calculated Column” from the top
toolbar. Name this column “Kinetic Energy” (KE for short) and give it units of “Joules.”
17. Its equation will be 1/2mv2, where m = the mass of the ball = 0.305 kg, and v is the vertical
velocity. You will enter 0.5*0.305*(variable Y)*(variable Y) as the equation.
18. To enter the total energy, again select “Data” and “New Calculated Column” from the top
toolbar. Name this column “Total Energy” (E for short) and give it units of “Joules.”
19. Its equation will be KE + PE, where KE is the kinetic energy and PE is the gravitational
potential energy. You will enter Gravitational Potential Energy + Kinetic Energy as the
equation.
20. You are now ready to plot all three energies on the same graph.
21. Select “Insert” and “Graph” from the main toolbar. A new graph appears.
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PHYS 205
SPR 2007
22. Double click the graph to see options for this graph. Change the title to “Energy vs Time.”
23. Select the “Axes Options” tab and select “Total Energy,” “Gravitational Potential Energy,”
and “Kinetic Energy” from the options. Make sure no other values are selected.
24. Change the vertical axis label to “Energy (J)”. Since you have more than one plot on this
graph, be sure to include a legend for the energies by selecting “Legend” from the “graph
Options” window.
25. Paste a copy of this completed graph in this document. Resize as necessary.
Questions:
 What happens to the ball’s kinetic energy as it rises and falls after a bounce?
 What happens to the ball’s potential energy as it rises and falls after a
bounce?
 What happens to its total mechanical energy as it rises and falls after a
bounce?
 The potential energy plot has the same shape as which other plot?
 Make a statement comparing the potential energy and kinetic energy graphs.
 What is represented by the abrupt “gaps” in the total energy plot?
 Find the approximate percentage of total energy that was conserved during
each of the bounces (divide the approximate total energy after a bounce by
the approximate total energy before the bounce).
 Does there appear to be a fairly constant percentage of energy conserved in
each bounce?
On a separate page:
A. Make statements comparing your pre-lab predictions with your actual findings.
B. Describe important concepts that can be gained/learned from analyzing these graphs.
Generate questions and provide answers to at least 3 important concepts related to each of
your 5 graphs (at least 15 total questions and answers)
Example: (Q): Why is the velocity-time graph comprised of straight line segments?
(A): the ball had a constant acceleration of g while in the air, both rising and falling
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