The first compasses were just lodestones — a naturally occurring magnetic ore — on small sticks placed in a bowl of water. This simple device pointed to the pole star and so was used, therefore, for navigation by early mariners. Shortly after the first compasses were used, people discovered that an iron or steel needle that had been touched or rubbed with a lodestone would also align with the pole star.

The Earth's magnetic field has a shape like a strong bar magnet placed near the center of the Earth with its S pole near the north geographic pole and its N pole near the south geographic pole. The Earth's magnetic field, which is three-dimensional, is inclined at about 11 degrees from its axis of rotation. A compass is just a magnet held on top of a pivot so the magnet can rotate freely. A compass points in a direction that lies along the magnetic field at the point. There is also a component of the magnetic field perpendicular to the surface of the Earth.

• Gather materials and make copies of the Find Your Own Direction-4th Grade Worksheet.
• Divide the class into teams of two students each.
• Hand out the worksheets.

1. Make an X in the center of the outside bottom of the bowl using electrical tape.
2. Fill the bowl with enough water (about half way) so that the compass paperclip will be able to move.
3. Cut a piece of thread about twice as long as the height of the water in the bowl. Tie one end loosely to a packing peanut. Tie the other end to a paper clip. Make sure the thread is neither too short (it is too short if it pulls the peanut under the water) nor too long (the thread and anchor allows the peanut to float to the sides of the bowl).
4. Magnetize the compass "needle" (straight pin) by stroking it one direction with the magnet (you will need to stroke it at least 20 times).

Figure 1. Compass for measuring Earth's magnetic field in a horizontal plane. click for copyright

5. Stick the compass needle (straight pin) through the center of a packing peanut with the paperclip "anchor."
6. Place the pin/peanut/paperclip assembly into the bowl of water (see Figure 1). What happens? (The magnetized straight pin should rotate to be oriented north/south. Verify orientation with a real compass.) Have students record answers on their Find Your Own Direction-4th Grade Worksheets.
7. Have students walk around the room with the compass they made. What happens to the compass needle as you move about the room? (Answer: it should always rotate so that it is pointed north/south.) Have students record answers on their worksheets.
8. Hold the compass flat near the top of any iron or steel object in the room (the most common steel objects in a classroom are filing cabinets and garbage cans, but any object than contains steel — small refrigerators or radiators, for example — will work). What happens when the compass is near the topmost part of the object? (Answer: the needle should point at the object.) Move the compass down to the bottom of the steel object, still holding it flat. What happens? (Answer: the needle should flip around 180 degrees.)

Discussion Questions: Solicit, integrate and summarize student responses.

• What if you knew you needed to head north to get to a relative's or friend's house, but you did not know which way is north? How would you proceed? (Possible answers: Look at where you are going, follow landmarks, use a map, use a compass.)
• How does a compass locate directions? (Answer: A compass indicates the magnetic field on the surface of the Earth and determines the direction.)

Prediction: Ask students to predict what will happen if we float a magnetized needle in water (Answer: The needle will point north.)

Worksheet: The attached Find Your Own Direction-4th Grade Worksheet allows students to record their observations during the activity.

Formation: Have students form a large "X" with groups of students pointing toward the four cardinal directions. Use the compass to resolve any directional disagreement among the students.