Pendulums

Lisa Ingram                      Frederick Douglass Middle Academy
                                 543 N. Waller
                                 Chicago IL 60644
                                 (312) 534-6176

Objective:

To determine the relationship of the frequency of vibration to the pendulum's 
length.

Materials Needed:

meter sticks (ring stands optional)
tape
string
objects of similar shape but different sizes pendulum bobs
stop watches
calculators

Strategy:

Presentation: 
    
    Ask students if they have ever seen a pendulum.  Make pictures available of 
different types of pendulums. 

Ask for two volunteers (a tall one and a short one).  Have these two people 
stand side by side.  Ask half of your class to count the amount of steps that 
the tall student takes.  Ask the other half to count the amount of steps the 
shorter student takes.  The two volunteers are to walk together (this is not a 
race).  Ask students to observe the results and discuss. (They should observe 
that the shorter person takes more steps than the taller student in order to 
keep up).  Discuss how the arm and the leg are pendulums.  The leg is attached 
and it goes back and forth when taking steps.  Discuss another type of pendulum 
that you see on a playground, the swing.  Discuss how the swing goes back and 
forth like a pendulum. (A picture of a swing is optional)  

Part B

Preparation:
Demonstrate to the students how to suspend the pendulum and how to count.  If 
necessary review the use of the stop watch.  Practice timing and counting a 
couple of times.

Equipment: 
The same lengths of string (60cm), pendulum bobs, stop watches, meter sticks. 

Procedure: 
The class is divided into fours' for this activity.  There should be a 
designated recorder, timer, counter, and swinger. First, the class will be 
instructed to take one of the objects and tie a string around it. Second, they 
should be given a location to tape down their meter stick.  Third, the students 
can began to do the following:  The recorder has paper and pen and is ready to 
write.  The timer has the stop watch at zero and is ready to time. The swinger 
is holding the pendulum at a suspension and will let the timer know when he/she 
will release. The pendulum will be timed for 10 swings.  (This means that the 
timer hits the start button, when the swinger saids release.  The counter will 
begin counting 1 when the pendulum comes back toward he/she.)  Each group will 
do this 3 times.  The recorder will write down the times and then average them 
with a calculator. A chart will be written on the board for each group to write 
down their calculations or timed vibrations. 

Conclusion: 
Students should take note that all of their calculations are very close, if not 
the same. Part B:  The same groups will repeat the exercise above, however, they 
will use different lengths of string (20, 40, 60, 80, 100cm).  Each group will 
be given their lengths of string to make new pendulums.  They will begin timing 
10 swings and recording.  This data will also be written on the board. (Students 
should began to see a difference in the calculations of the other groups 
vibrations).  The teacher will graph the timed vibrations on the board.  The 
vibrations on the x-axis and the length of string on the y-axis.   As an extra 
visual aide, the teacher can tape the actual pendulum of each group on the graph 
and discuss. 

Performance Assessment:
Each group will be given two worksheets to complete.  On the first worksheet
will be two questions. They are the following:  1st - Compare your timed
vibration calculations (by looking at the graph on the board) to the other
groups.  Write down your observations.
2nd - Compare your timed vibrations again (by looking at the graph on the 
board) to the other groups.  Write down your observations.
The second sheet will be done individually and it asks the following:
 - What affects the vibration of a pendulum?