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Activity: Modeling Amphidromic Points
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts
NGSS Disciplinary Core Ideas

Amphidromic points are places where the tidal range (difference in height between high and low tide) is zero compared with other areas in the basin.



  • Table 6.1
  • Ruler
  • Wood skewer or other long probe
  • Cylindrical container
  • Water
  • Permanent marker
  • Food coloring
  • Towels




  1. Using the ruler and a marker, mark the wood skewer every 1 cm.



Fig. 6.13.1. Diagram of container with three X’s marking locations to place depth probes.

Image by Fan Yang

  1. Use a marker to place an “X” in the center of the container, at the edge of the container, and then halfway between these points (Fig. 6.13.1).
  2. Fill the container approximately half way with water. Add a few drops of food coloring to the water.


  1. In your model, you will gently swirl the water around in the container. Consider what will happen to the water level in the container as you swirl the container. Make predictions about what you expect the water level will be in the container above the ‘X’s drawn in Step 2 as the container is swirled.
    1. Fill in the ‘Prediction’ column of Table 6.1.
    2. Make a prediction about which of the ‘X’s would be closest to the amphidromic point.
  2. While one group member gently swirls the container in a clockwise or counterclockwise motion, take water depth readings using your wooden skewer at each of the ‘X’ positions in the container.
    1. Fill in the “Trial 1” column of Table 6.1.
    2. Repeat twice more filling in the next two columns of your chart
    3. Calculate the average depth


Activity Questions
  1. Why is it important to take several measurements at each ‘X’ position in the procedure?
  2. Did your water level predictions match your observations?
  3. Where was the amphidromic point in the container? Did it match your predictions?
  4. How did this activity model tidal movement in an ocean basin?
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.