Student Exploration: Ripple Tank ALL ANSWERS 100% CORRECT FALL-2021 GUARANTEED GRADE A+

Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. The image below shows small ripples, or waves, moving through water in a pond. BOLD the description below that you think describes the motion of a wave most accurately. A. Each wave consists of a set of water molecules moving outward from the center. B. When a wave passes, water molecules move up and down before returning to near their original position. 2. Waves have crests (high points) and troughs (low points). The wavelength of a wave is the distance between adjacent crests (or troughs). Label the crests, the trough, and the wavelength on the image at left. Click the image on the left, then click Edit. Use the available tools to draw your labels then click Save & Close. Gizmo Warm-up A ripple tank, such as the one shown in the Ripple Tank GizmoTM, is a shallow pan of water with a vibrating motor that produces waves. The tank is lit from above so that the wave crests and troughs are visible. Ripple tanks are particularly useful because many properties of water waves are shared by other kinds of waves that are harder to see. Check that Open tank is selected and the Wavelength is 4.0 cm. Click Play ( ) and observe. Click Pause ( ) when the first wave reaches the right edge of the tank. 1. The light regions represent troughs while the dark areas represent crests. About how much simulation time does it take the wave to cross the tank? 2. Click Reset ( ). Set the Wavelength to 16.0 cm, and click Play. Click Pause when the waves reach the edge. How did increasing the wavelength affect the shape and speed of the waves? Question: What causes wave motion? 1. Predict: In this activity, you will test two hypotheses for wave motion. Circle the hypothesis you think is closest to the truth. Hypothesis 1: Waves are sets of particles moving together due to their forward momentum. Hypothesis 2: Waves occur when particles transmit energy to other particles in all directions but don’t move far from their original positions. 2. Make connections: The hypothesis describes how some materials flow. For example, consider the mudslide shown at left. Compared to point A, point B is nearly three times farther from where the mudslide landed at the bottom of the mountain. Why did the mudslide miss point A but hit point B? Which hypothesis is demonstrated by the motion of the mud? 3. Predict: The Gizmo shows a barrier with a small gap that waves can pass through. Points A and B are equal distances from the gap. A. If hypothesis 1 is true, which point do you think will be hit by a wave first? Explain. B. If hypothesis 2 is true, which point do you think will be hit by a wave first? Explain. 4. Observe: Check that the Wavelength is 9.0 cm, the Wave strength is 1.20, and the waves are Planar. Drag arrows (found on the left side of the Gizmo) to the positions of points A and B on the diagram. Press Play. Click Pause when the first wave reaches point A. A. What do you notice about the shape of the wave after it passes through the barrier? B. Do the waves reach point A first, point B first, or do they reach points A and B at about the same time? 5. Infer: What do your observations suggest regarding the two hypotheses? The ability of waves to spread from a point such as the gap in the barrier is called diffraction. This ability allows waves to turn corners in ways that individual particles cannot. The fact that waves reached point B at the same time as point A demonstrates that waves in water move differently from the mud in the landslide. 6. Challenge: Water waves are caused by individual water molecules moving back-and-forth and up-and-down locally. Because the particles do not move in sync, water piles up in some places and troughs appear in other places. The individual molecules themselves do not move very far compared to the wave we see. Water piled up in one region (a crest), tends to drain into nearby regions. In fact, each individual point on a crest can be thought of as the source of a new wave. This idea, called Huygens’ Principle, was discovered by the great 17th-century Dutch physicist Christiaan Huygens. Use Huygens’ Principle to explain how water waves can diffract.