Encompassed by Forces

Activity Time: 30 minutes
Recommended Grades: 1 - 8
Objective: Create a working compass using everyday materials. Then, design and conduct an experiment to test the accuracy of your homemade compass.

  • Magnet
  • Needle (a 1” segment of a metal paperclip can also be used)
  • Dish, approximately 6 inches in diameter or larger (such as a pie plate)
  • Water
  • Slice of cork or disc cut out from bottom of Styrofoam cup (essentially, a small object that will float)
  • Optional: reliable compass
  1. It is important to first properly magnetize the needle that will be used. To magnetize the needle, rub the magnet along one side of the needle in the same direction (not back and forth) for approximately 30 seconds.
  2. Fill your dish with 1 inch of water and place it on a flat surface.
  3. If using a cork, push the needle through the edge of the cork, so that you have about the same length of needle exposed on each side. If using a Styrofoam disc, lay the needle (or paperclip) flat on top.
  4. Place your float in your dish of water and observe. If the needle moves, as expected, construct an explanation for what happened. Where do you think the needle is pointing? If the needle did not move, define the problem and design a solution. Was your needle properly magnetized?
  5. Once you have a working model, develop and conduct an experiment to test the accuracy of your device. As a suggestion, use a standard compass and compare readings. You can also use your knowledge of the movement of the sun (rises in east, sets in west) to determine where north is located. If available, a map of your home with a compass rose can also be used.

The rotational movement of liquid iron in the earth’s core generates electric fields, which in turn produces the earth’s magnetic field. Although the force this field exerts is weak in comparison to forces such as gravity or friction, it is strong enough to have an effect on magnets (such as the magnetized needle). In order to do so, however, we must reduce friction as much as possible. This is where the float comes in. By floating the magnet on water, we create a nearly frictionless surface. This allows the magnet to rotate freely. The magnet will align itself with the earth’s magnetic field, thus pointing toward the magnetic North Pole.

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