CLASS COPY – For your own copy, find this document under “Physics - Labs.”
CONSERVATION OF MECHANICAL ENERGY LAB
PART I – MEASURING POTENTIAL ENERGY
Purpose: To determine the relationship between height and potential energy for an object.
Materials:
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Lab Quest with USB Connector Cord
Playground Ball
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Motion Detector
Computer with LoggerPro Software
Important Equations:
Procedure:
1. Set up the computer, Lab Quest, and Motion Detector so that the detector can be on the floor at
least 80 cm away from the edge of the table.
2. Connect the Lab Quest to the computer using the USB connector cord. The smaller end is plugged
into the top of the Lab Quest and the USB side is plugged into the computer.
3. Open Logger Pro from the desktop icon on the computer. Open the File menu → select Open → find
the _Physics with Vernier folder → open the “16 Energy of a Tossed Ball” file.
4. We need to enter the mass of the ball into the computer's program formulas for Potential Energy
and Kinetic Energy. The "default" mass in the computer is 0.155kg. Double click on the box in the
lower right corner of the screen that displays the mass and change the value to 0.324 kg (the mass
of the playground ball).
5. You should see two graphs. The top graph is Position vs. Time. Change the bottom graph to
Potential Energy vs. Time by clicking on the "Velocity" axis and choosing Potential Energy instead.
Also, change the maximum potential energy value to 10 J by double clicking on the y-axis,
selecting the “Axes Options” tab, and changing the top value to 10.
6. Hold the ball from the sides starting 0.5 m above the detector. Hit "Collect" and slowly raise the
ball at a constant speed as high as you can reach. INDIVIDUALY create and label both
quantitative graphs on a SEPARATE SHEET OF PAPER with appropriate titles and axes labels.
Analysis Questions:
1. Do the two graphs look similar? Why might you expect these results?
2. At what location would the ball have to be for it to have a potential energy measurement of zero?
3. If instead of raising the ball upwards, you drop it from some height and let it fall towards the
detector, how will the potential energy (EP) change during the fall? The kinetic energy (EK)? The
total mechanical energy (ME)? Explain your answers for each situation.
4. PREDICT (with sketches) what a Potential Energy vs. Time graph, a Kinetic Energy vs. Time graph,
and a Total ME vs. Time graph would look like for an object dropped freely from some initial height
by sketching these graphs on your separate sheet of paper.
PART II – MEASURING THE POTENTIAL, KINETIC, AND TOTAL MECHANICAL ENERGIES
Purpose: To observe the relationship between potential energy, kinetic energy, and total mechanical
energy for a falling object.
Procedure:
1. Click on the y-axis of the top graph to change it to Total Energy vs. Time. Click on the
bottom graph's y-axis, select “More” and make sure both boxes are checked for Kinetic
Energy and Potential Energy. The bottom graph should now graph both Potential Energy
and Kinetic Energy vs. Time.
2. Change the maximum y-axis values for both graphs to 7 J, and the maximum time value on
the x-axis to 1 s by double-clicking on the axes (see Step 5 from Part I).
3. Have one group member in position to drop the playground ball and another member
should be ready to catch it BEFORE it hits the sensor! Practice dropping and catching a
few times before you collect data.
4. Press the green "Collect" button in the top-right side of the screen. The dropper should
drop the ball as soon as they hear the clicking sound coming from the motion detector.
5. Have your teacher check your graphs if you think they are good ones. Once they are
approved, INDIVIDUALY create and label both quantitative graphs on your SEPARATE SHEET
OF GRAPH PAPER with appropriate titles and axes labels.
Analysis Questions (CONTINUED FROM PART I):
5. Why does the Potential/Kinetic Energy graph look as it does? What is the relationship
between Potential and Kinetic Energy? Explain in detail.
6. Why does the Mechanical Energy graph look the way it does? Explain in detail.
7. Could you say Energy is "conserved" during the fall? Explain in detail.