Key concepts
Magnetism
Tools
Earth's poles

From National Science Education Standards: Ability to distinguish between natural and human-made objects

Introduction
Have you ever wondered how a compass works? Traditional compasses (not the digital kind found in smart phones and other devices) are tools that take advantage of a natural feature of Earth: the planet's magnetic poles. With a compass, you can find out which way a magnetic pole is—and from that, you can approximate other directions such as where south, east and west are as well.

Compasses might seem complicated, and the magnetic poles of the Earth might seem very far away. But you can build a working compass at home! Below is an easy way to tap into the Earth's magnetic field—and help orient yourself in the process.

Background
Earth has a magnetic field around it, which is called the magnetosphere. It is based around the two magnetic poles, located near the North and South Poles. People have been using this natural phenomenon for hundreds of years to help navigate. Just by slightly magnetizing a small metal object, such as a sewing needle, you can make it sensitive to this otherwise invisible force.

Handheld electronic devices, such as smart phones now often include GPS (global positioning systems) to display a digital compass. These work by finding your location and orientation relative to an imaginary "grid" and satellite positions, rather than sensing the Earth's magnetic field.

Materials
•    Plastic bowl or wide plastic cup
•    Sheet of blank paper
•    Round cork from a bottle
•    Scissors or sharp knife (to cut the cork)
•    Sewing needle
•    Magnet
•    Water

Preparation
•    Cut your paper into four pieces, and label each one with a cardinal direction (North, South, East or West).
•    Carefully cut off a circular piece of cork about half an inch thick.
•    Fill the bowl or cup with water so that you can easily reach the surface.

Procedure
•    Carefully holding the sewing needle by the eye (with the point facing away from you), swipe it along one side of the magnet in the same direction 30 to 40 times (this action makes the needle magnetic).
•    If you want to test the needle's magnetism, see if it will attract a straight pin. If the magnetized needle picks up the pin, it should be ready to be your compass needle.
•    Carefully push the needle through the middle of the piece of cork lengthwise, so that the needle is parallel to the circle ends of the cork (rather than up and down, or perpendicularly).
•    Before you put the finishing touch on your compass, predict which direction is north. Which way do you think the needle tip will point? Place your "North" label down on that side of the bowl.
•    Place the cork on the top of the water with one of the circle sides down so that the needle is parallel to the surface of the water.
•    Let go of the cork. What does the needle do? Which way does the tip point? You've found magnetic north!
•    Which way is south? What about east and west? Place your labels accordingly.

Read on for observations, results and more resources.

Observations and results
Were you able to determine which direction magnetic north is? Can you find the other cardinal directions?

If you followed the compass to the north, you would not actually end up at the North Pole because the magnetic poles of the Earth move slowly over time (the current magnetic north is near an island in far northern Canada called Ellef Ringnes Island).

When you ran the needle along the magnet in the same direction, you were making the needle itself magnetic. Many metals contain small clusters of material that are like tiny magnets, but normally these clusters point in different directions, canceling each other out. In that case, the metal object itself does not have an overall magnetic tendency. By running the needle against the magnet in one direction, however, you aligned these small clusters within the needle to face the same direction. You gave the needle itself a single magnetic direction.

Why don't magnets move to align themselves with the magnetic field? Generally the force of gravity and any friction they have on the surface are too strong. But the needle in a compass, such as yours, faces little resistance, so it is free to point in the direction of the magnetic field.

Humans are the only animals that make compasses, but some animals, such as sea turtles, seem to use the Earth's magnetic fields to help them find their way during long migrations. Scientists have found small pieces of magnetite (which is a magnetic substance) in the heads of some animals, which might help them know which way north is. But researchers are still trying to understand exactly how such migration works.

Cleanup
Carefully remove the needle from the cork. Pour out the water.

More to explore
"The Earth Has More Than One North Pole" from Scientific American
"Magnetic Fields Guide Turtle Hatchlings across the Ocean and Back" from Scientific American
"Magnetism" overview from NASA's Goddard Space Flight Center
"Pigeons Detect Magnetic Fields" from the University of Washington
What Makes a Magnet? by Franklyn M. Branley, ages 4–8
Janice VanCleave's Magnets: Mind-boggling experiments you can turn into science fair projects by Janice VanCleave, ages 9–12

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