LAB Xi: DAMPING MOTION                

Problem: What is the relationship between the height  that a ball bounces and the number of times it bounces?

Background:  To oscillate means to pass from one state to another and back again.  A swinging pendulum is one example of an oscillating body. Another example would be a vibrating string on a musical instrument.  Can you think of other examples?  Many oscillating systems are said to undergo harmonic motion. Many things in nature exhibit harmonic motion.  Can you think where this type of motion occurs in your body? 

If we set a pendulum in motion it stops after a period of time.  A vibrating string on an instrument also slowly stops. This decline of motion is referred to as damped harmonic motion.  Today you will study one simple example of damped harmonic motion.  That of a bouncing ball.

Try to determine what type of relationship you expect to observe today.

State your hypothesis. Justify your statement!

Materials: ping pong ball, rubber ball, meter stick

Procedure:  Hold a ball at a distance of one meter from the surface of the table (diagram I). Drop the ball.  Catch it after one bounce.  Measure its height.  Drop it again, and let it bounce twice.  Measure the height after two bounces.  Repeat this procedure at least five more times.  Be sure to repeat the complete procedure at least three times, averaging your results (see class notes). Record all data in results.

Repeat if time permits using the rubber ball.

Results:

Table I:  Ping pong ball

Number of bounces              height (cm.)

      0

      1

      2

      3

      4

      5

      6

      7

Table II.  Rubber ball

Number of bounces              height (cm.)

      0

      1

      2

      3

      4

      5

      6

      7

Graphs:  On the same graph make two plots.  Plot I: plot number of bounces on the x axis and height on the y axis for the ping pong ball.  Plot II: plot number of bounces on the x axis and height on the y axis for the rubber ball.

Discussion extra: Design an experiment to study the effects  different materials would have on determining the height a ball bounces. Can a ball ever return to its starting point on the first bounce? Why? Try to determine a relationship that fits your data points. 

1) What are the independent and dependent variables?

2) How are the variables changing with relationship to each other?

3) What happens to the dependent variable when the independent variable increases? decreases?

4) How does the relationship shown in this experiment compare with other relationships you have so far seen?

5) How does the equation for this relationship compare with those of other equations you have studied?

Applications: