Handbook of Nature-Study · Lesson CCXIX · Topic 34: The magnet
219. The magnet
Goal: Your child finds out what magnets attract, where they are strongest, how like and unlike poles act, and makes a working compass from a needle.
You'll need
- A bar magnet and a horseshoe magnet (ordinary toy-strength magnets)
- Iron nails, paper clips, steel pins, brass tacks or coins, and a few non-metal things
- A long sewing needle, a slice of cork and a shallow bowl of water
- A small compass
- Iron filings in a sealed zip bag (optional)
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
The lesson has a leading thought, a method listing magnets, compass, lodestone, nails, filings and tacks, and eighteen observations: where magnets are strongest, chains of tacks, like and unlike poles, magnetizing a needle, floating needles on corks, the compass, the pattern of iron filings, and lodestone.
The lesson, step by step
Safety first
Use ordinary magnets. Small, very strong magnets (and magnet toys with tiny pieces) are dangerous around young children: two swallowed magnets can pinch the intestines together. Keep magnets away from phones, computers and bank cards. Needles and pins are sharp; an adult hands them out. Keep iron filings sealed in a bag so they can't get in eyes.
The leading thought
Any substance that will attract iron is called a magnet, and the force which enables it to attract iron is called magnetism. This force resides chiefly at the ends of magnets, called the poles.
What does it pick up?
Let your child test everything, as the book says, "during play time."
Of what substance are the objects made which the magnets can pick up? Does a magnet pick up as many iron filings at its middle as at its ends? What does this show?
Chains, pushes and pulls
Pick up a tack with a magnet. Hang another tack to this one end to end. How many tacks will it thus hold?
Pull off the tack which is next to the magnet. Do the other tacks continue to hold together? Why?
Use small nails or paper clips.
Bring two ends of two bar magnets together; do they hold fast to each other? Change ends with one, now do the two magnets cling more or less closely than before?
Make a compass
Magnetize a knitting needle or a long sewing needle by rubbing one end of a magnet along its length twelve times, always in the same direction, and not back and forth.
Push the needle through a slice of cork (an adult does this) and float it in the bowl of water.
When it finally rests does it point north and south or east and west?
Check with the real compass.
Pictures of force
Place fine iron filings on a pane of glass or on a stiff paper. Pass a magnet underneath; what forms do the filings assume?
Use the sealed bag of filings over the magnet. It shows the same pattern with no mess.
What we know now
Comstock is right that the Earth is a giant magnet, and that the pole near the North Pole is, by magnet rules, a south pole, since it pulls the north end of a compass. Today we know that pole is not at the North Pole itself and slowly wanders; a compass points to it, so maps give a small correction for each place.
Nature notebook
Draw the bar magnet with the filing pattern around it. Make a two-column list: "magnet picks up" and "magnet doesn't pick up."
Answers to the book's problems
Magnets pick up iron and steel (and nickel), not brass, copper, aluminum, paper or wood; the filings cluster at the ends, so the force is strongest at the poles. A tack touching a magnet becomes a magnet itself, so it can hold another; pull the first away and the chain falls apart. Like poles push apart; unlike poles pull together. The floating needle settles pointing north and south. The filings make curved lines running from one pole around to the other.
Worked out for this site from the scan. If a number in your copy differs, trust the book.