Physical Science Name:______

Unit 8 - Lab #3 Energy of Falling Motion

Investigating Energy and Falling Motion

Background Information

When an object such as a ball falls, it accelerates and acquires kinetic energy, or energy of motion. If it does not reach terminal velocity, it acquires its maximum velocity and therefore its maximum kinetic energy just as it hits the ground. At that point, its motion is stopped and it is compressed. The kinetic energy is momentarily converted to potential energy, or stored energy. This potential energy is then converted back to kinetic energy as the ball bounces back. No ball will return to the exact height from which it was dropped because some of the kinetic energy is converted to other forms of energy, such as heat, when the ball strikes the ground. According to an important principle known as the law of conservation of energy, however, the total amount of energy does not change

Problem

How can the motion of a bouncing ball be described and accounted for in terms of energy?

Materials

Meter stick

Tennis ball

Ping-Pong ball ball

Golf ball

Marble

50

40

30 Figure 1

20

ground 10

Procedure

·  Mass each of the four objects being tested in this activity and record the mass on the data table.

·  Have one member of your group hold the meterstick upright with the zero mark on the floor, as shown in Figure 1.

·  Have a second member of your group drop the tennis ball from the top of the meterstick (100cm mark) in such a way that it does not touch the meterstick on the way down.

·  Have a third member of your group note the height of the first bounce. The bounce height should be called out to the fourth member of the group, who should record it in the Data Table. Let the ball continue to bounce and continue observing it for as long as you can. (It may take several trials because the ball may tend to bounce away from the meterstick.)

·  Repeat steps 1, 2, and 3 for all four of the objects.

·  Make a separate graph for each of the objects tested. Plot the height of each bounce on one axis, and the bounce number (i.e. bounce #1, bounce #2 , etc.) on the other axis. Which is the independent and which is dependent variable?

Data Table

Type of Ball / Mass of object / First
Bounce / Second
Bounce / Third
Bounce / Fourth
Bounce / Fifth Bounce
Tennis Ball
Ping-Pong Ball
Golf Ball
Marble

Analysis:

1.) Which ball retained the greatest percentage of its mechanical energy (had the

most elastic collision) on the first bounce? Be sure to show your calculations of PE at 100cm and height of 1st bounce. Then calculate the percentage retained.

2.) Explain the shape of each line on the graphs in terms of energy. Why were the

shapes similar? Were there any graphs that differed greatly from the others?

Explain why the differences might have occurred.

3.) Why can’t a ball bounce higher than the height from which it is dropped?

Explain your answer in terms of energy.

4.) Suppose you had carried out this investigation using a carpeted floor. How

would your results have differed? Be sure to explain your answer in terms of

energy conservation.

5.) Is there a relationship between the mass of an object and its ability to retain

mechanical energy? Explain your answer using your data and graphs.

The percentages from question #1 could be helpful.

6.) Draw 4 bounces of the superball and use arrow to indicate the transfer of

KE to PE to KE, etc.

7.) Explain why all the balls ended with no energy. Where did it go and how do

you know this?

8.) Calculate the PE of each ball at the 100.00cm mark and the KE of each ball

at the 25.00cm mark as it falls. Remember that total ME in a system is equal to PE + KE. Assume no energy lost due to air resistance. You must show all work for full credit

Ball / PE (100.00cm) / KE(25.00cm)
Tennis Ball
Ping-Pong Ball
Golf Ball
Marble

Conclusions:

What did you do? What did you find? What generalizations can you make?

1