Use from Refuse-Build a Compass

Materials:

Wide mouth glass jar (rinsed clean and dry), stiff paper (like an index card-preferably a piece of paper that you would normally throw away instead of a new piece of paper), darning needle, thread, pencil, a real compass, bar magnet

• Obtain a clean, wide-mouth glass jar (one that would normally be thrown away, or hopefully recycled!)

• Cut a circle out of a piece of stiff paper. Make the diameter of the circle about half the diameter of the inside of your jar.

• Magnetize a darning needle by stroking it several times with a bar magnet. Stroke from the center of the needle to its end. Test the magnetized needle by placing it near a real compass or an iron or steel surface, such as a file cabinet, and observing that there is an attractive force.

• Carefully place the needle through the paper as shown in the diagram. It will need to balance, so make certain that the needle is centered (the center of the needle will need to be at the center of the paper).

• Use thread and a pencil to suspend the needle and stiff paper apparatus you have just made inside the jar. Make certain that the apparatus does not touch the sides of the jar.

• Test your homemade compass by comparing the direction of your hanging needle to the direction of a needle in a real compass.

Questions for students:
(1) If you turn the jar through 90°, does the needle also turn through 90°? Why or why not?

(2) What happens if your compass is placed close to a metal file cabinet?

(3) What happens if the real compass is brought close to your compass?

(4) Do compasses point exactly north at all locations on the Earth?