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Activity: Simulate Deep-Water, Transitional, and Shallow-Water Waves

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Materials

  • Fig. 4.18
  • Fig. 4.21
  • Fig. 4.22
  • Table 4.9
  • Table 4.10 (optional)
  • Long wave tank
  • One paddle that fits snugly in the width of the wave tank
  • Water
  • Three rulers
  • Masking tape
  • Wood blocks or books
  • Four corks or other small buoyant objects 1 cm in diameter
  • Monofilament line
  • Two small lead sinkers
  • Sand
  • Towels
  • Dry-erase marker, felt-tip marker, or grease pencil
  • Food coloring (optional)
  • Plastic pipette (optional)

 

Procedure

Safety Note: When raising the wave tank, make sure the tank and table are secure. Place towels around the tank to clean up any splashing water. Immediately mop up all water spills to prevent slipping.

  1. Set up the long wave tank as shown in Fig. 4.22.
    1. Place wood blocks or books to raise one end of the table the tank is sitting on. The height you will need to raise the table depends on the size of your tank.
    2. If the wave tank is heavy and/or the table is smooth, set the wave tank on a towel to increase friction and prevent it from sliding off.
    3. Tape one ruler to the end of the wave tank as a backstop. The backstop should be positioned to prevent the paddle from going past vertical.
    4. Tape a second ruler along the top edge of the wave tank (the yellow ruler in Fig. 4.22)
    5. Tape a third ruler 5 cm in front of the backstop as the paddle-stop. The paddle-stop will help you control the amount of water pushed by limiting the distance the paddle can move.

<p><strong>Fig. 4.22.</strong> Wave tank set up for simulating deep-water, transitional, and shallow-water waves. (This image is not to scale; the paddle, paddlestop, and ruler have been enlarged relative to the size of the tank.)</p><br />


  1. Fill the wave tank with water so only two-thirds of the length of the tank is submerged.
     
  2. Create and observe waves that begin in the deep side of the tank and break on the shore of the shallow end of the tank. You may have to adjust the amount of water in the tank and the elevation of one end of the tank.
     
  3. Model particles at surface, bottom, and mid-water level in the deep and shallow ends of your tank. Additional options for materials are listed in Table 4.10 of the Orbital Motion of Waves activity.
    1. Place two free-floating corks on the water, one over the deeper section, and the other over the shallower section.
    2. Tie sinkers to the two other corks with monofilament line so that the corks hang near mid-water level. Put one cork in the deep section, the other in the shallow section of the tank.
    3. Sprinkle some sand into the deep section and some into the shallow section.
       
  4. Generate waves to compare the movement of particles in waves at the deep and shallow ends of your tank.
    1. Generate waves by rocking the paddle back and froth.
    2. Observe the movements of the corks and the sand.
      1. Try to observe each of the following for deep-water waves: (1) the circular motion of wave energy near the surface and (2) the lack of motion near the bottom.
      2. Try to observe each of the following for shallow-water waves: (1) the elongated motion of wave energy near the surface and (2) the side-to-side dragging motion near the bottom.
    3. With a marker or a grease pencil, trace onto the side of the tank the movements of the corks and the sand at the surface, at midwater, and at the bottom of the tank.
       
  5. (Optional) Use food coloring to observe the motion of water in the water column at the deep and shallow ends of your tank.
    1. Use a plastic pipette to insert drops of food coloring into the water column (mid-water) at the deep-water and shallow-water sections of the wave tank.
    2. Generate waves by rocking the paddle back and froth.
    3. Observe the movement of the food coloring before it mixes.
       
  6. Make sketches showing the water movement in deep-water and in shallow-water waves (see Fig. 4.18 and Fig. 4.21).

<p><strong>Fig. 4.18.</strong> (<strong>A</strong>) If a small buoy (black circle) was on the surface of the water, it would move in a circular motion, returning to its original location due to the orbital motion of waves in deep water. (<strong>B</strong>) As deep-water waves approach shore and become shallow-water waves, circular motion is distorted as interaction with the bottom occurs.</p><br />
<p><strong>Fig. 4.21.</strong> Wave tank set up for observing orbital wave motion. (This image is not to scale; the paddle, paddlestop, and ruler have been enlarged relative to the size of the tank.)</p><br />


 

Activity Questions: 
  1. Describe what happens to a wave as it changes from a deep-water to a shallow-water wave.
    1. How does the shape of the wave crest change?
    2. How does the wavelength change?
    3. How does the speed of the wave change?
    4. How does the movement of water in the wave change at the surface? In mid-water? At the bottom?
       
  2. What types of waves did you observe in the tank? See Fig. 4.21 and Table 4.9 for information to support your answer.
     
  3. Why might it be difficult to generate deep-water waves in a wave tank?
     
  4. How is your wave tank model similar to real waves breaking on a shore? How is it different? How can it be improved?
     
  5. Explain the difference between deep-water and shallow-water waves.
     
  6. When surfing, what features of a wave might a surfer look for in deciding which one to catch? Base your answer on what you know about how waves change as the water depth changes.
     
  7. By observing waves, what can you tell about water depth and the ocean bottom?
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.