CECsci.171


TITLE:    Simple Harmonic Motion

AUTHOR:   Lauren Tanner, Barnett Elementary.
          Payson, UT

GRADE LEVEL: 4-6

OVERVIEW:  Simple harmonic motion (SHM) is a special type of
regular oscillation.  It is a common and familiar phenomenon
and occurs whenever an object that is in equilibrium (under
the action of forces) is disturbed slightly from its
equilibrium position.  There are many simple demonstrations
of SHM that can be done as hands-on experiments that will
show this phenomenon clearly.

PURPOSE:  The purpose of this lesson is to help students
understand the theory of simple harmonic motion (SHM) by
performing hands-on, practical application experiments.

OBJECTIVES:  Each student will demonstrate SHM by performing
a series of demonstrations of regular oscillation and
explaining the theory behind the experiment to a partner.

RESOURCES/MATERIALS: metronome, strings of various lengths,
bobs of different weights, diving board, World Book Science
Book, Physics Today p.54-55.

Terms:   kinetic energy          momentum
         potential energy        harmonic motion
         oscillation             friction
         acceleration
         gravity
         force

ACTIVITIES AND PROCEDURES:
1.   The pendulum -
     Show the movement of a simple pendulum bob and explain
     SHM.  When the bob is hanging downward it is in
     equilibrium position.  When it is disturbed, it
     executes SHM.  Gravity pulls it back to equilibrium
     position but momentum carries it past that position to
     another point.  It relies on acceleration due to
     gravity to deep swinging.  Try different lengths of
     string and different weights of bobs and see what
     happens.  Which moves slower, a heavy bob or a light
     bob?  What difference in acceleration is observed due
     to length of string? What else did you observe?
2.   The metronome -
     This inverted compound pendulum executes SHM when set
     into motion by a force.  The period of swing can be
     altered by varying the position of the small weight on
     the arm of the metronome.  How does the weight set near
     the top of the arm affect the swing of the arm, faster
     or slower?  What happens when the weight is moved to
     the bottom of the arm?  Is the swing equal on each side
     of the position of equilibrium?
3.   A diving board -
     This oscillates with SHM after the diver has started
     into his dive.  Before this when the diver is bouncing
     to gain maximum height, the board undergoes forced
     oscillation.  Observe a diver as he makes a dive, or
     set up a simulation of a  dive in the classroom.
Can you think of any other practical applications of SHM?

TYING IT ALL TOGETHER:
Take a visit to Hansen Planetarium (Salt Lake City, Utah) or
any other science museum that may have a swinging pendulum.
Explain the movement of the pendulum in relation to the
rotation of the earth.  This is a fine example of SHM.
While there go to a star show!