`How to speed up a slow Grandfather - The PendulumArthur Hermann                 Fiske Middle School                               6145 S. Ingleside Avenue                               Chicago IL 60637                               (312) 535-0991Objectives:To introduce the concept of periodic motion and relate it to its use in a  Grandfather type clock.  To discover that the period of a pendulum is dependenton the length of the pendulum and independent of the weight of the bob and theamplitude.  Students will discover that a slow running Grandfather clock can becorrected by changing the length of the pendulum.Materials:Each group needs a stop watch, pendulum and metal washers.Materials needed for a pendulum are string and paper clip.To make a play Grandfather clock you will need a ringstand and a rod and a   clockface made from paper. Strategy:                                    Begin the class by saying "I'm sure your all wondering why I called you here at this time.  In my hand I hold a memo from our CEO that threatens our jobs.  We have been given one hour to solve a problem that a has caused a hugh drop in sales."  Point to the play clock.  "As you can see our clock is five minutes slow.  In a moment we will break into our work groups and start working on possible solutions to our problem: What can be done to the pendulum to have the clock run on time?"  At this time you may want a student to come to the front to point out the pivot point, length, and bob.  Be sure to demonstrate what a cycle is and how to count cycles.  Next pass out a pretend memo from the OLD TYME CLOCK CORP.  The memo should state the problem and indicate they may be fired if they do not solve the problem by the end of the period.  Each group is given a different length of string to create a pendulum.  Lengths may vary from 25cm to 2m.  Each group will find the time for their pendulum for 20 cycles.  On the board draw a graph with numbers across the top indicating time in seconds.  Start with zero using 5 second periods, up to 50 seconds. When the students have found the number of seconds per 20 cycles ask the students to come forward and tape their pendulum at the appropriate time. Once all the groups have taped their pendulum to the graph, discuss the results.  Students will hopefully see the direct relationship between the length and the period of time.  Next, each group is given a string of the same length, but this time students may add different numbers of washers.  As before the groups will find the period of their pendulum and then come to the front to tape their pendulum on another graph.  Hopefully the students will understand the idea that the weight of the bob does not influence the period of the pendulum.  Lastly, you should demonstrate the effect of amplitude on a pendulum.  You could probably do this in front with help of a student.  At this point you should compare the three variables; length, weight and amplitude.  Using the collected data ask the students to write their solution to correcting the problem of the slow grandfather clock.                                                                   Performance Assessment:       This activity will take more than one period, a good place to break would be after finding the effect of length on a pendulum.  For assessment, students should be able to describe what should done to the pendulum and explain how this would solve the problem.  The student's understanding of this material can be evaluated by having them predict what the correct length would be for the clock to kept the correct time.  Hopefully by experimenting students will discover the length at 20 seconds is the correct length.  `