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Activity: Floating Magnetic Compass

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:


  • Permanent magnet
  • Sewing needle
  • Paper cup
  • Water
  • Small piece of Styrofoam or cork
  • Petri dish (top or bottom)
  • Indicator Disk (Fig. 8.13)
  • Permanent marker
  • Paper towel


  1. Fill the cup with water to about 1 cm from the top.
    <p><strong>Fig. 8.12.</strong> (<strong>A</strong>) Magnetize a needle by rubbing its tip against a magnet. (<strong>B</strong>) Float the magnetized needle in a cup of water after sticking it through a piece of Styrofoam.</p>
  2. Magnetize a sewing needle by pressing the south pole of a permanent magnet against the center of the needle and gently stroking the magnet four or five times towards the point (Fig. 8.12 A).
  3. Insert the needle through, or place it on top of, a small piece of Styrofoam or cork to make a needle-float assembly.
  4. Place the needle-float assembly onto the surface of the water to see if it floats (Fig. 8.12 B). Adjust if necessary until the needle floats satisfactorily. Make sure the permanent magnet is not near your needle-float assembly.
  5. Locate magnetic north (N) by allowing the needle to rotate until it stops. Mark this reference point on the cup with a thick line. This is your indicator arrow.
  6. Using the indicator disk (Fig 8.13), mark the bottom of a Petri dish every 30° with a permanent marker. Label the marks with degrees of the compass (0° to 330°) and directions north (N), south (S), east (E) and west (W) as shown in Fig. 8.14. Put the labeled Petri dish over the cup with the 0° mark aligned over the point of the floating needle.


<p><strong>Fig. 8.13.</strong> Indicator disk for a floating-needle compass</p> <p><strong>Fig. 8.14.</strong> Use the indicator disk to label the petri dish on the floating-needle compass.</p>

  1. Use the compass to find directions.
    1. Hold the compass with the indicator disk directly in front of you with the needle pointing forward and to the north.
    2. Make a right-angle (90°) by turning to your left.
    3. Turn the indicator disk until 0° (360°) is over the point of the needle.
    4. In which direction are you facing—N, S, E, or W? What is the compass bearing—the direction in the number of degrees from north?
    5. Choose a new object to face in the room and spin to face in that direction. Answer the questions in step 8.
  2. Determine your direction using the compass.
    1. Hold the compass with the indicator disk directly in front of you with the needle pointing forward and to the north.
    2. Look at your indicator disk. Turn the disk so that the 240° mark is aligned with the compass needle tip.
    3. Rotate your body until the needle tip once again lines up with 0° N. You are now oriented 240°. In what direction are you facing?
    4. Choose a new angle to face. Turn the disk so that your chosen angle is aligned with compass needle tip. Rotate your body until the needle tip once again lines up with 0° N. What direction are you facing?
  3. Practice using the compass to give directions.
    1. Write the directions for walking in a square.
    2. Test your directions by having your lab partner follow them using the compass as a guide.
  4. Repeat step 9 for a triangle and for another geometric shape.
  5. Locate your seat in the classroom by triangulation.
    1. Using a full page of paper, sketch your classroom.
    2. Using your compass, locate the points on the walls that line up north and south. On your sketch, draw these points, connect them, and label them.
    3. Locate two objects that are not along the same line of sight. Draw these objects on your sketch.
    4. Determine the compass bearing for each of these objects. Record them below the sketches of the objects.
    5. Draw lines across your sketch along the bearing line for each object.
    6. The place where the lines cross is your position. Mark this with a star.
    7. Have another member of the class verify that your position is correct.


Activity Questions: 
  1. Did you have any difficulties using your compass? If so, what steps did you take to resolve them?
  2. How could you improve your compass?
  3. Were you able to successfully instruct your partner to walk a path using the compass headings? Explain your answer.
    1. Did you change your method of giving instructions during the activity? If yes, why?
    2. How could you improve your instruction-giving process?
  4. Do you think you could you use a floating-needle compass aboard a ship? Why or why not?
    1. What problems would you have to solve to make it practical?
    2. What modifications would you make?
  5. Was your classmate able to verify your position in step 11? Why or why not?
  6. How is using a compass different from using GPS?
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.