AskERIC Lesson Plans
Lesson Plan #:AELP-PHY0049


An AskERIC Lesson Plan

AUTHOR: Vilia Natchez; Our Lady of Snows, NV



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.


 The purpose of this lesson is to give children a basic understanding of the physical properties of waves without becoming too technical.


 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. 1 slinky
  2. 2 radios
  3. 1 toy xylophone
  4. * 5-6 test tubes mounted in a rack (jars/glasses)
  5. rubber bands
  6. empty containers (boxes, plastic cups, lids)
  7. * 6-8 yd. masking/strapping tape
  8. 1 glass pie pan
  9. 1 food color (2-3 drops)
  10. 1 overhead projector
  11. * plastic straws (80-100)
  12. * bottled soap bubbles with wand (1)
  13. * 1/4 cup clay (approx.)
  14. * toothpicks (approx. 12)
  15. 1 flat pan
  16. * aluminum foil (3x3") square
  17. * straight pins (1)
  18. 1 lamp (no shade) or flashlight

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

  1. 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.
  2. 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.
  3. 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
  1. 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.
  2. 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
  1. 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.
  2. 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.
  3. 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.

 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.

May 1994

These lesson plans are the result of the work of the teachers who have attended the Columbia Education Center's Summer Workshop. CEC is a consortium of teacher from 14 western states dedicated to improving the quality of education in the rural, western, United States, and particularly the quality of math and science Education. CEC uses Big Sky Telegraph as the hub of their telecommunications network that allows the participating teachers to stay in contact with their trainers and peers that they have met at the Workshops.

This activity has been copied, with permission, from the Educational Resources Information Center (ERIC) server to ours, to allow faster access from our website. We encourage you to explore the original site.

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