CONSERVATION OF ENERGY

Rolling Down the Hill

In this week's lab, we will investigate conservation of mechanical energy as an adventurous volunteer on a bicycle coasts down the hill near the CA building. The cyclist will make 3 runs keeping a good streamline profile and then make 3 runs in an upright position to create as much air resistance as possible.

Each group will:

• Devise a method to detemine the vertical height from the bottom of the hill to the top. You will have access to long tape measures, protracters, levels, straight sticks and anything else in lab.
  Note: There may be no absolute horizontal or vertical references nearby. Take this into account when devising your method.

• Devise a method to measure the speed of the bicycle (and cyclist) at the bottom of the hill. You will have access to stopwatches, traffic cones and tape measures.

Your group should discuss your methods and equipment requirements with the instructor before starting. Each group is to determine the height of the hill independently. Make as many measurements as time permits. The velocity of the cyclist at the bottom will also be done independently by each group. However, there will be only one cyclist, so you will take data for the same runs.

Report:

Every student will hand in their own report. In addition to the normal requirements for a report, be sure this report also includes the following:

1. Describe concisely your methods for measuring the height of the hill and the velocity of the cyclist at the bottom.
2. For both sets of data (streamlined and non-streamlined), find the average final velocity. Find the changes in the PE and KE and determine the percentage of the average mechanical energy "lost" in each case.
3. Compare the results of the energy loss for both cases above. Based upon this comparison, comment on the importance of air resistance in this experiment? Do you think it could account for all energy losses? What else could produce energy losses.
4. Based upon the accuracy and consistency of your mesurements, make a numerical estimate of the error in your calculations of PE and KE. (The error estimates should take into account not only the precision of your intruments but the spread of values in the data as well.) Is the error large enough to account for apparent energy losses? Explain.
5. Discuss any other sources that you think might contribute to a discrepancy between changes in the PE and KE.