TITLE: UNDERSTANDING WAVES
AUTHOR: Vilia Natchez; Our Lady of Snows, NV
GRADE LEVEL/SUBJECT: 3-5 Waves
OVERVIEW:
Sound, water and light travel in waves. All three have troughs
and crests. Sound is a disturbance of air waves with pitch. Water
waves travel in a circle away from the source of disturbance. Light
waves travel in a straight line unless they meet an obstacle.
Experiments in this unit may be built upon or deleted in order to
fit the time frame (1-3 lessons) desired.
PURPOSE: The purpose of this lesson is to give children a basic
understanding of the physical properties of waves without becoming
too technical.
OBJECTIVES:
Children are to understand the terms "crest " and "trough" as
related to waves. They are to use a hands-on method using toys to
become aware that waves are in air, water and light.
RESOURCES/MATERIALS:
(* items indicate items needed per group)
1 slinky
2 radios
1 toy xylophone
* 5-6 test tubes mounted in a rack (jars/glasses)
rubber bands
empty containers (boxes, plastic cups, lids)
* 6-8 yd. masking/strapping tape
1 glass pie pan
1 food color (2-3 drops)
1 overhead projector
* plastic straws (80-100)
* bottled soap bubbles with wand (1)
* 1/4 cup clay (approx.)
* toothpicks (approx. 12)
1 flat pan
* aluminum foil (3x3") square
* straight pins (1)
1 lamp (no shade) or flashlight
ACTIVITIES AND PROCEDURES:
A demonstration is made with a slinky. Ask children to define
the part they think of as a crest and that part which is a trough.
Draw a simple diagram on the board, labeling each. A dictionary
could be used. Explain that all waves have crests (ups) and troughs
(downs).
Crests and Troughs in Sound Waves
I. Tune in two radios to the same station. Place them
about 50 cm apart. Have children walk quietly about
the room listening for dead spots (troughs) and
loud spots (crests). They could be encouraged to
raise a hand when they hit a trough.
II. Listen to different pitches on a toy xylophone.
Ask why they think it sounds different. They
should be allowed to try the ready-made xylophone,
then make their own. A xylophone is easily
made by pouring different levels of water into
a rack, by using identical jars, etc. .
After trying both the ready-made and the homemade
versions, they should be guided to conclude that
the length of bar or height of water can regulate
the pitch of sound waves.
III. Rubber bands of various thicknesses can be
stretched across boxes or any small, empty
containers. See if they can make graduated
sounds as in a xylophone. Conclusion: The
tighter a band is stretched, the faster it
vibrates and makes a higher sound.
Crests and Troughs in Water Waves
I. A glass pie pan is mounted on an overhead
projector. It is filled with water tinted
with food coloring. Waves can be demonstrated
by touching a rod/pencil to the center of the
water and watching the waves (troughs and crests)
move to the edge of the pan and back. Try two
rods to see what happens when the waves meet.
Encourage the children to try it. Ask if they
have ever seen this happen before. Relate this
to a rock thrown into a pond or a toy into a swimming
pool.
II. Wave machines can be made by groups of children to
demonstrate what they did in the above experiment.
It also simulates ocean waves. A strip of tape
(3-4 ft.) is laid on a table sticky side up. A
child should hold each end securely. Others in
the group will place the middle of a straw each
half inch in the middle of the tape. When all
straws are laid, the second strip of tape is
placed on top of the straws (sticky side down)
and above the first strip of tape. The finished
product will resemble a spine (tape) and ribs
(straws). A child holds each tape end horizontally
while a third child pushes down on one end of
the wave machine's straws allowing a wave pattern
to go from one end of the straws to the other. Be
sure to look for waves and troughs!
Crests and Troughs in Light Waves
I. Blow bubbles with the wand. Look for colors in
them. Why are they colored? Explain that light
waves travel in a straight line unless something
interferes with them. Since bubbles are round and
not straight, light waves get bent when they hit
the bubble. Many bending waves cause color.
II. Give each child or group a small square of aluminum
foil (3x3) and a straight pin. Instruct them
to make two tiny holes near the center of the foil
about 1/2cm apart. A bright light source without
a shade (lamp, flashlight) should be set in front
of the room and all other lights turned out. The
children should hold the foil about one foot in
front of their eyes. Closing one eye and looking
through both holes, they should see one light
source diffusing crests and troughs of light.
III. The last experiment could be related to math in
that it requires the children to guess the number
of planes that are in a constructed object. They
might start by constructing a simple square. This
is easily achieved by placing four small balls of
clay so they are connected with four toothpicks
forming a square. Ask how many planes (flat
surfaces) are in the figure. When they have made
suggestions, dip the figure into a pan of the
bubbles. Lifting it carefully, one plane can be
observed. Their next figures can be more complex
(3-D) which will make plane estimates more complicated.
Always be aware of the light waves visible on each plane.
TYING IT ALL TOGETHER: This is a series of very simple hands-on
experiments which will introduce children to the idea that waves
have troughs and crests. They should be comfortable with those
terms even though they don't remember those of " bending" or
"diffusion". It will be a firm base for physics in their later years.
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John Kurilecjmk@ofcn.org