PHYS 1401 – General Physics I

Energy Transformations

Leader: _____________________________ Recorder: ___________________________

Skeptic: _____________________________ Encourager: _________________________

Materials

Laptop

LabPro

Motion Detector

Bouncing Ball

Introduction

In this activity we will investigate energy transformation in a bouncing ball as it falls freely, and then after it has bounced. We will determine different types of energy and examine how they are related.

Review Questions

R1) How do you determine the gravitational potential energy of an object?

R2) How do you determine the kinetic energy of an object?

R3) How do you determine the mechanical energy of the object.

Procedure

We will employ the motion detector to obtain data for this lab. The experimental set up is shown in figure 1.

Figure 1 Schematic of experimental set up

1. Set Up

Clamp the motion detector so that it faces down, is level, and is as high as possible above the floor. Connect the motion detector to DIG/SONIC 1 of the LabPro.

Make sure that the LabPro is connected to the computer and has power and then start up LoggerPro. Open the experiment file by following the path “Probes and Sensors”=>”Motion Detector”=>”Motion Detector”.

2. Set up the coordinate system

We want to measure the potential energy so that it is zero at the floor. Click on experiment, then Set up Sensors. Click on LabPro1 and the following box will appear.

Click on the icon for the motion detector and then click on Reverse Direction. With nothing between the detector and the floor, click on the zero button. The motion detector will now read position measured from the ground with the positive direction being up.

3. Determine the mass of the ball

Use the digital scale to determine the mass of the ball in kg.

mass of ball = ___________ kg

4. Data Acquisition

You only need one good data run for this experiment. Click on collect and drop the ball directly underneath the motion detector. Make sure that no part of the person releasing the ball obscures the motion detector’s view off the ball. The ball should bounce several times, and these bounces should be very clear in the graph of position vs. time. If you can’t see at least several bounces, drop again. Try to release the ball so that it drops straight down and move the detector if you hit a rough spot on the floor.

Questions

Q4) Sketch the graph of the position vs. time for several bounces.

Q5) Describe in words what the graph you sketched in Q4) is showing.

D6) Make a new column labeled Gravitational Potential Energy by clicking on Data, then New Calculated Column. Enter the appropriate formula for the gravitational potential energy. Choose Position from the list of Variables (Columns) for the height of the ball.

D7) Display the Potential Energy v. time.

Q8) How does the graph of potential energy vs. time compare to the graph of position vs. time? Explain why this is the case.

D9) Make a new column labeled Kinetic Energy by clicking on Data, then New Calculated Column. Enter the appropriate expression for the kinetic energy of the ball.

D10) Display the graph of kinetic energy vs. time.

Q11) How does the graph of kinetic energy vs. time compare to the graph of potential energy vs. time. Be specific.

D12) Make a new column labeled Mechanical Energy by clicking on Data, then New Calculated Column. Enter the appropriate expression for the mechanical energy of the ball. Note that the previous columns that you defined will now appear in the list of Variables.

D13) Display the Graph of Mechanical energy vs. time.

Q14) Sketch a graph of the mechanical energy vs. time in the space below.

Q15) Describe the appearance of the mechanical energy vs. time graph while the ball is in the air between bounces.

Q16) What does your answer to Q15) say about the mechanical energy while the ball is in the air between bounces?

Q17) What happens to the amount of mechanical energy after each bounce?

Q18) What should be the sign of the change in mechanical energy after each bounce? Explain.

Q19) Where does the mechanical energy lost as a result of each bounce go?

D20) Use the STAT button to find the average value of the mechanical energy for each bounce. Complete the following table. E is the mechanical energy. ΔE is the amount of mechanical energy lost during the bounce, and E_thermal = - ΣΔE is the amount of thermal energy that was added. Note that the Σ in the preceding formula means that you add up the ΔE’s to get the total amount of mechanical energy that was converted to thermal at that point.

Time in Air	E (J)	ΔE (J)	E_thermal (J)	E_total = E + E_thermal (J)
1		0	0
2
3
4

D21) Display a graph showing Gravitational Potential Energy, Kinetic Energy, and Mechanical Energy on the same y-axis vs. time. Print and attach the graph.

Q22) Is the last column in the table constant? What does that mean about the total energy of the system of ball and floor.

Q23) Write a few sentences explaining how the gravitational, kinetic, and mechanical energy are related while the ball is in the air between bounces. Be sure to describe how each is changing and relate it to the others.

Q24) Write a few sentences describing how the mechanical energy changes between bounces, what happens to that energy, and what happens to the total amount of energy during the process.