Mechanical Equivalence of Heat Energy

Goal: Measure a temperature change due to mechanical energy expnditure

Materials

• Two large styrofoam soup cups
• Thermometer
• Dense metal (lead shot or fishing weights, coins)
• Cardboard tube at least 2 feet long (to act as guide and measure for the drop)

  The drop should be as long as possible. If you can construct a tube that will support a drop of two to three meters, your noticeable heat change will be more reliable.

• Water

Suggested Procedure

1. Fill one styrofoam cup with water, but leave room to add weights.
2. Add a measured amount of water to the second styrofoam cup (do not fill more than half full).
3. Measure and record the temperature of the water.
4. Measure the mass of the weights you will drop.
5. Place the weights in the first styrofoam cup and allow weights and water to come to room temperature.
6. Assemble the tube above the second styrofoam cup to act as a guide for the drop. Make sure all the weights will fall into the cup.
7. Take the temperature of the water in the second cup.
8. Remove the weights from their water bath and drop them into the second cup using the tube as a guide. Record the amount of mass dropped and the distance they fall.
9. Measure the temperature of the water (including the weights).
10. Repeat your procedure several times.

Data Handling

1. Determine an appropriate table layout to record distance for fall, volume of water and its mass, mass of the weights dropped, starting and final temperature of water in second cup.
2. Add columns to calculate temperature difference and calculate the amount of heat required to raise the measured amount of water by the temperature difference using q = mC * ΔT.
3. Determine the potential energy change of the dropped mass using PE = mgh.
4. Compare the mechanical energy change (PE) and the heat energy change.

Report

1. Use the guidelines for lab reports to prepare a formal report of your work.

Post your report to the Lab thread at the Moodle.

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