**Fig. 5.11.** Ripple tank with X’s marked on bottom.

Image by Byron Inouye

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## Materials for Parts A–B

## Procedure

Title

Activity: Wave Patterns in a Ripple Tank

NGSS Science and Engineering Practices

NGSS Crosscutting Concepts

NGSS Disciplinary Core Ideas

Table of Contents

**Fig. 5.11.** Ripple tank with X’s marked on bottom.

Image by Byron Inouye

- Fig. 5.11
- Ripple tank or shallow pan
- Water
- Ruler
- Grease pencil or marker
- Metronome or sound recording
- Small solid waterproof objects
- Table 5.2 (optional)
- Towels

**A. Observe wave interference patterns.**

Recall from the topic Sea States in the unit Waves that interference occurs when two or more wave sets meet. Constructive interference occurs when the wave crests and troughs meet, increasing the amplitude of the combined wave. Destructive interference occurs when the crests from one wave set and the troughs from another wave set meet, and the waves cancel each other out.

- Measure length of the tank with a ruler. Divide the length of the tank by four. Using a grease pencil or marker, place two “X” marks on the bottom of the tank along a center line at one-quarter and three-quarters of the way across the tank (Fig. 5.11).

- Fill the pan halfway with water.

- Using your knowledge of wave properties, predict what will happen when you and a partner tap the water at the X’s to create waves in the ripple tank. Draw a diagram of what the wave pattern will look like from above the tank.

- Practice creating identical wave patterns with your partner by tapping on the surface of the water above each X. Use a metronome to help you tap the water at the same rate and time.

- Observe the waves propagating across the tank from each X. Draw a diagram of your observations.

**B. Demonstrate reflection, refractions and diffraction.**

- Using the ripple tank and waterproof objects, create wave patterns that demonstrate reflection.
- Predict how you can demonstrate reflection. Draw your predications.
- Test your predictions and refine your methods until you are able to demonstrate reflection.
- Draw a diagram of your final setup for demonstrating reflection.

- Repeat Part B Step 1 for both refraction and diffraction.

- (Optional) Model additional types of wave patterns from Table 5.2.

Activity Questions

- Did your observations match your predictions in Part A? Explain your answer.

- What type(s) of interference did you observe? Use your knowledge of wave properties to describe what is occurring at areas in the ripple tank where you observed interference.

- How were you able to demonstrate reflection, refraction, and diffraction?

- Did your observations match your predictions in Part B? Explain your answer.

- How can you account for the observation that, no matter what the direction of incoming waves, they become more parallel to the shoreline as they approach land?

- What effects would a sudden shallow area or a sudden deeper area have on incoming shallow-water waves?

- A point is a narrow piece of land projecting into the ocean. What is meant by the saying "the points always draw waves"?

- Some sailors use waves to detect an island long before they can see it. How do you think this is possible?

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.