Demagnetize: Does Hitting a Magnet Weaken Its Magnetic Strength?

Problem

Does hitting a magnet weaken its magnetic strength?

Materials

• iron nail
• bar magnet
• small paper clip
• compass
• wooden block
• masking tape
• adult helper
• hammer

Procedure

NOTE: Never touch a compass with a magnet. Touching a compass with a strong magnet can change the polarity of the compass needle, causing the end marked north to become a south pole and all directions to be reversed.

1. Magnetize the nail by laying it on the magnet for three minutes.
2. Test the magnetic properties of the nail by touching it to the paper clip. The nail has been magnetized if the clip clings to it.
3. Lay the compass next to the wooden block.
4. Lay the magnetized nail on the wooden block so that the point of the nail faces east.
5. Tape the nail to the block.
6. Ask an adult to strike the nail 20 times with a hammer.
7. Test the magnetic properties of the nail again by touching it to the paper clip.

Results

The paper clip does not cling to the nail after the nail has been struck by the hammer.

Why?

Atoms within a magnet do not act individually, but combine to form groups called domains. Atoms within the domain act like tiny magnets and line up with their north ends pointing toward the earth's magnetic north pole. When many of these microscopic groupings of atomic magnets (domains) line up with their north poles in the same direction, a material becomes magnetic. Hitting the magnetized nail causes the orderly arrangement of the domains to be jarred out of place. The north poles randomly point in different directions. The nail loses its magnetic properties, and is said to be demagnetized. Turning the nail in an east-to-west direction prevents the domains from lining up with the earth's magnetic force field, which lies in a north-to-south direction.

Let's Explore

1. Does the nail have to be struck 20 times to demagnetize it? Repeat the experiment, leaving the tip of the nail hanging over the edge of the wooden block so that it can be touched to a paper clip after each strike with the hammer. Record the least number of strikes required to demagnetize the nail. Science Fair Hint: Diagrams showing the position of domains before and after hitting the nail can be used as part of a project display.
2. Would laying the nail in a north-to-south direction affect its ease of being demagnetized? Repeat the original experiment, placing the nail in a north-to-south direction. Again place the tip of the nail over the edge of the wooden block, and touch it to a paper clip after each hammer strike. Compare the number of strikes to the number needed to demagnetize the nail in an east-to-west direction.

Show Time!

Can you also demagnetize a nail by rubbing it back and forth with a magnet? Magnetize a nail and test its magnetism by touching it to a paper clip. Rub a magnet back and forth across the surface of the nail five or six times, and test the nail's magnetic properties again. Display a diagram showing the procedure of this experiment and indicate the results. Remember that demagnetized materials have domains pointing in random directions.

Check It Out!

Find out more about ways to reduce or destroy the magnetic properties of a magnet. Would cutting a magnet in half. destroy it? How does heat affect magnetic properties? Do magnets lose their strength over periods of time?

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Janice VanCleave's Magnets
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