Study Guides | 4. electromagnetism | Magnetism

Study Guide: Magnetism

Vocabulary

• Magnet
• Lodestone
• Magnetism
• Magnetite
• Magnetic Force
• Direction of Force
• North and South Poles
• Iron
• Compass

Demonstrations

1. Floating paper clip
2. What kinds of objects are attracted to magnets?
3. Iron filings
4. Finding north by making a compass
5. Magnetic springs
6. Magnetic cannon
7. Magnetic levitation
8. Cooking with magnetism

Magnet

A magnet is a rock or a piece of metal that can attract other types of metal toward itself. The metals iron, steel, nickel, and cobalt make good magnets.

It’s possible that the original magnets were created when chunks of iron-rich minerals were magnetized by the electrical charge in lightning.

We can make a new magnet by rubbing an existing magnet against another piece of metal. The new piece of metal must be continuously rubbed in the same direction. This will cause all the electrons in the new metal to spin in the same direction.

Magnetic Force

The force of magnets—called magnetism—is one of the basic forces of nature, along with electricity and gravity. Magnetism is an invisible force that works over a distances and through other objects. A magnet does not have to touch an object to attract it.

Magnetism is caused by the unique properties within certain materials. In most objects, electrons spin in random directions. However, in magnets the molecules are arranged so that their electrons all spin in the same direction.

This creates two poles in a magnet, a North-seeking pole and a South-seeking pole. The magnetic forces between the two poles of a magnet create a magnetic field. A magnetic field surrounds all magnets.

The Magnetic Earth

The Earth is a giant magnet. Scientists do not fully understand why, but they think the movement of molten metal in the Earth’s outer core generates electric currents. These currents create a magnetic field with invisible lines of force that flow between the Earth’s North and South Poles.

The Earth’s magnetic field is important for life on Earth. Birds, whales and other animals use the Earth’s magnetic field to find their way over long migrations. Humans developed the compass for the same purpose.

Perhaps the most important feature of the Earth’s magnetic field is that it deflects much of the Sun’s solar wind and radiation. Without this, we would not be able ot live on the Earth. Some particles from the Solar Wind leak through. When these tiny particles hit atoms of gas in the upper atmosphere near the geomagnetic poles, they produce light displays called auroras.

The Compass

Long ago, the ancient Chinese discovered naturally magnetic stones called “lodestones,” and around 400 BCE, they began using these stones to create the first compasses. However, at first they were used to orient a person to a right relationship with the universe.

In time, the Chinese found that they could make a needle magnetic by stroking it against a lodestone, and that the needle would then point north-south.

It was not until many centuries later that the compass was used for navigation, but once it was the idea caught on fast. The compass proved to be the most important invention in the history of navigation. By the 14th century, many other civilizations were using the compass as well, including the Vikings, Mongols, Hindus, Greeks and Muslims.

Observations

1. Magnets attract and are attracted to other magnets.
2. Magnets attract the metals iron, steel, nickel, and cobalt.
3. The attractive and repulsive power of a magnet is concentrated at the poles.
4. Unlike poles attract each other; like poles repulse each other.
5. Magnetic force can travel through many objects.
6. The Earth is a giant magnet.
7. The Earth’s magnetic field protects us from the Solar Wind.
8. The compass is the most important invention in the history of navigation.

Some Questions

1. In which direction does a compass point when it is placed directly over the North Pole?
2. Which ancient civilizations first discovered the lodestone and compass?
3. What protects the Earth from the Solar Winds?
4. What causes a material to become magnetic?
5. How do scientists explain why the Earth is a magnet?
6. How do scientists think the first lodestones were formed?