Some familiarity with electrons and atoms.

Who can tell me what a magnet is? (Listen to a number of answers from the class). Those are all great answers! Well, today we are going to talk about what makes a magnet, and how engineers use magnets to store information.

Can anyone think of something that we use to store information? (Possible answers: Computer, flash drive, hard drive, floppy disk.) You're right! And guess what! Not everyone realizes this, but most of the electronic devices that you just named use magnets to store information! That's pretty neat, isn't it? Who knows why it is important for us to be able to record and store information? (Possible answers: So we can keep track of important information and access it later). Right! Here's another question for you — who designs, tests and builds devices that use magnets (such as computers or flash drives)? Here's a hint — it starts with an "E"! That's right — engineers do! Engineers need to understand how magnets work so that they can make neat devices that help people and make our lives easier or better in many ways.

What makes a magnet? Did you know that magnets are actually created by tiny spinning electrons in an atom? The electrons in an atom are in constant motion. The electrons move about the nucleus and spin like a top, creating a tiny magnetic field (space around the magnet where magnetic forces can be noticed). If electrons are spinning in the same direction there is more magnetism, while electrons spinning in opposite directions cancel out each others' magnetic fields. Magnetic fields are invisible; we can only see the effects of the magnetic force.

Also, all magnets have a north pole (N) and a south pole (S). These names are used because if a bar magnet is suspended freely in the air, one end always points northward in the earth's magnetic field, while the other points southward. Unlike poles attract each other and stick together (S and N) while like poles push each other away (N and N, or S and S).

There are also special magnets called electromagnets. These magnets are created by wrapping a coil of wire around a magnetic material, usually iron or steel, and running electricity through it. The electric current turns the magnetic material in the middle of the coil into a magnet.

This idea of using magnets to store information is called magnetic memory storage. It is actually a pretty simple idea. Here's how it works: Inside a computer hard drive are disks called platters. The platters are coated with a material similar to rust. When this material is exposed to a magnet, it becomes magnetized. Many little electromagnets are used to arrange, or "write" the magnetism into specific patterns, and recognize, or "read" it. These little electromagnets are called "read/write heads." They are located on an arm that moves above the disk, or platter. The position of all the little electromagnet heads in the arm over the top of the platter allows them to read and write information to the disk. Some devices that use magnetic memory storage are computers, flash drives, and zip or floppy disks. Credit, debit and ATM cards also have magnetic information storage on the dark strip on one side. The magnetic strips contain bank and account information.

Magnets come in many different shapes and sizes. Many of the magnets used in machines are actually electromagnets rather than permanent magnets. The magnetic field of an electromagnet can be turned on and off as you turn the electricity to the coiled wire on and off. However, even though we call them "permanent," permanent magnets are not really permanent either. They can be de-magnetized by hitting them with a hammer or heating them up. Why do you think that engineers would rather use a magnet you can turn on and off instead of a permanent magnet? (Answer: You can demagnetize a permanent magnet by hitting or heating it, which makes it useless.)

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If you place a permanent magnet near something that provides magnetic storage, such as a hard drive, it erases the memory or stored information! By contrast, an electromagnet can only erase memory when it is turned on. Do you know some other objects that you need to be careful not to expose to magnets? (Possible answers: Credit cards, cassette tapes, computer disks, and televisions.) This is because a magnet can erase the memory of those items as well. Today, we are learning about one use of magnets — magnetic storage. Engineers use magnets in all sorts of devices including motors, appliances and magnetic storage!

What can you tell me about a magnet? (Possible answers: It has north and south poles, it is caused by spinning electrons, it can stick things together or push them apart, it can store information or erase information, etc.) What is an electromagnet? (Answer: It is a magnet that is made when electricity is pushed through a coil of wire around a magnetic material.) How are electromagnets and permanent magnets different? (Answer: You can turn an electromagnet on and off.) Do you remember how you can demagnetize a magnet? (Answer: By heating or dropping/hammering it hard.) What is one way we talked about today that engineers use magnets? (Answer: For magnetic memory or information storage.) Can you think of any examples of magnetic memory storage? (Answers: Computer hard drives, zip disks, flash drives.)

Have the students build a magnetometer to monitor the earth's magnetic field. See the Soda Bottle magnetometer at http://image.gsfc.nasa.gov/poetry/workbook/magnet.html or another version at http://www.windows.ucar.edu/tour/link=/teacher_resources/magnetometer_edu.html.

For a math extension, have students learn how to write numbers in the binary number system. A good resource is the Binary Math page at http://computer.howstuffworks.com/bytes7.htm.

Have students make drawings to explain the orientation of earth's magnetic field and the direction a compass would point when located at various places on earth.