Let's Make Waves

Science Activity

Background
Many children hold misconceptions about the nature of water waves. One common misconception is that waves are generated from within the water. Although that may appear to be true, most waves -- and certainly the waves most children see -- are actually generated by wind. As wind travels across the water's surface, it pushes against the water and energy in the wind is absorbed by the water.

Another common misconception is that as a wave moves the water itself moves with the wave. In fact, a wave is the movement of energy through water. The water moves up and down, but not sideways in the direction of the wave's motion. The energy from wind moves in the direction of the wind. The energy moves from water molecule to water molecule, making each molecule move in a small circle. When one molecule bangs into its neighboring molecule, energy transfers to that neighboring molecule.

The most effective way to help children replace a misconception is to give them an experience that directly challenges it. In this simple set of activities children use wind to create waves and use marbles to model energy moving through water.

WHAT YOU'LL NEED

• 1 large, flat pan, about 4 or 5 inches deep, for each group (dishpans or larger)
• 1 electric table fan or paper fan for each group
• buckets or jugs for filling the pans with water
• food dye (optional)
• 5 large marbles or ball bearings for each group

WHAT TO DO

1. Ask the class what causes waves. Discuss their ideas.

2. Put the pans on tables and fill each pan with 2-3 inches of water.

3. Divide students into as many groups as you have pans and put each group around a pan.

4. About 1 foot from each pan (on a narrow side), place an electric fan or have a student hold a paper fan facing the pan.

5. Ask students to predict what will happen when the fan blows across the water's surface. After students have made predictions, let each fan blow at a low speed.

6. Have students report the results. Were there waves? Did the water bunch up at the far end of the pan? Did the water slosh out of the pan? Then speed up the fans and have students report again. Make sure students don't run fans so quickly that water sloshes out of the pans. (It might slosh out with the fan at high speed because the energy in the waves can't transfer into the pan's wall readily.)

7. Discuss with the class the connection between the wind and the waves. Ask students to guess why the water didn't bunch up at the far end of each pan.

8. Give each group a set of 5 marbles. Have students place 4 of the marbles on a table, lined up in a row with each marble touching its neighbors. Ask students to predict what will happen if the fifth marble is gently rolled at the marble at one end of the row. After students have made predictions, have one student in each group roll the fifth marble. The marble at the far end of the row will roll away and the others will not move. Have students repeat the experiment several times.

9. Discuss the idea that the energy in the rolling marble went into the marble it hit, and from that marble to the next, until the energy reached the last marble. The energy made that marble roll away. Wave energy moves through water the same way.

10. Bring the students together for a wrap-up discussion. Ask them what causes waves. Discuss their answers, relating the answers to the wave experiment. Ask them if water moves sideways inside a wave, or if the water stays in one place while the wave moves through it. Discuss the answers, relating the answers to the wave experiment and to the marble experiment.