Compasses

Background

The Chinese used magnetite (they called it tzuh shih, or loving stone, for its attractive properties) to develop north-south pointing devices as early as 200 B.C. Court magicians entertained royalty using magnetic spoons that would always point in the same direction. In England, these rocks were called lodestone (lode meaning to guide). In 1269, Peter Peregrinus documented the following characteristics that all magnets display:

1. Magnetic fields can act at a distance.
2. Magnets can only act on other magnetic materials.
3. Opposite poles attract and like poles repel.
4. When suspended, north poles point north and south poles point south.

With these observations, European sailors were able to navigate using needles that were magnetized by lodestone. Their north-south orientation was used for navigation, though the Chinese used these stones to create compasses a few centuries earlier.

Why do this in your classroom?

• To encourage the following process skills for scientific investigation: prediction, observation, developing a hypothesis and drawing conclusions.
• To help students understand the relationship between electricity and magnetism.
• To allow students to manipulate variables and record changes.
• To encourage problem solving abilities.

Materials

• String
• Sewing needle
• Paperclip
• Bowl
• Water
• Magnet
• Various magnetic materials
• Various objects that float

Procedure

To create a compass you need to allow a magnet to be suspended so it can turn freely. There are many ways to do this.

With string:

1. Hang a string from the middle of a doorway.
2. Tie a bar magnet to the string so it is evenly balanced. As it turns, it will settle and point north-south.

With string:

1. Magnetize a small object such as a paperclip or sewing needle. Do this by placing one end of the magnet against one end of the needle or paperclip.
2. Fill a bowl with water.
3. Float the magnetized needle or paperclip very carefully on the surface of the water.
4. If you are having a hard time doing this, try placing the needle inside a small section of a straw, on a piece of cork, or on anything that will help it float.
5. There are multiple solutions possible for this activity. Any magnetized object that is floating will become a compass. Give your students some options and see what they come up with.

What's happening?

Every magnet has a north-seeking and south-seeking pole. If two magnets are brought together, the north pole of one will attract the south pole of the other. This is why compasses work on the Earth. The Earth’s magnetic field, although weak, is strong enough to make the north pole of a free floating magnet align with the magnetic pole of the planet. The magnet’s north pole will point to Earth’s north, which means that the Earth’s geographic North Pole is the opposite of its magnetic north pole! In other words, the planet’s geographic North Pole is its magnetic south pole, and vice ve

Science in Other Subjects

Lessons with compasses extend beyond science class. Since a compass is used for navigation and to show direction, try using a compass in geography class. Students could use a compass to navigate around the school during a special scavenger hunt or outside on the playground or fields. 

Video

For more information contact MagLab educator Carlos R. Villa.