Making a Compass
Every now and then people get mixed up in their directions. If you asked a dozen people which direction is north, they might all point in different directions. Right now, as you are reading this, can you point to the north? Are you sure you are right?
It has always been important to know directions. You can’t travel long distances by air or sea without being sure of them. Hunters, trappers, explorers, and others must be sure of their directions. The magnetic compass is an instrument that has been used for thousands of years by people all over the world to help find their way.
Suppose you point to the direction that you think is north. Now you can make sure you are right if you know how to use the things that are pictured here.
You probably have seen small magnets that are shaped like the horseshoe magnet in the picture. Magnets have other shapes too. Sometimes they are shaped like a U, and sometimes like a bar. The bar magnet is like the horseshoe and U-magnet except that it is straight. All magnets are much alike, no matter what shape they are. They all pull things made of iron and steel toward them. They all have two ends or poles. One is called a north pole and the other a south pole. Some can pick up heavier things than others. That is because some have a stronger force than others. This force is called magnetism. This magnetism is strongest at the poles of a magnet, and weaker in the part between the poles.
It you nave a magnet, you can make another magnet from it. For examole, if you have a magnet, you can make another magnet from an iron pin. (Some pins are brass and won’t work.) You can do this by rubbing the pin on the magnet several times. Then you can test the pin to see if it is a magnet. You can do this by trying to pick up another iron pin with the one you have been rubbing on the magnet.
Why don’t you try this?
There is a very interesting thing about a straight magnet like a bar magnet. If you hang it up by a thread so that it can swing around easily, it will stop swinging around after a while and point north and south. A steel needle will do that, too, if it is made into a magnet.
First make the needle (a big one about two inches long is best) into a magnet by rubbing it on one end of the bar magnet. Don’t rub it back and forth or sideways. Rub the needle in one direction only from the center to the end of the magnet, holding it parallel to the magnet. Rub it hard and rub it twenty or more times. Now try to pick up an iron pin with the needle. If it picks it up, you know that you have made the needle into a magnet.
Can you think what you might do next? You want to fix the needle so that it can swing around easily, so you lay the flat piece of cork on the water in the glass dish, and then gently lay the needle into the groove in the cork so it won’t roll off. (If you can’t find a cork, pry the cork liner out of the cap of a pop bottle.) Take the magnet away so that it won’t pull the steel needle. If it does, your compass will not be accurate. Keep the cork in the middle of the dish of water so it can swing around easily. Watch it. Does it stop swinging around? Move it around and see if it stops in the same position. Try making another needle into a magnet. Put it in place of the first needle. Does it stop in the same position as the first needle you made into a magnet?
If you have been careful in following the directions, your needle will stop when it is pointing north and south. One end or pole of the needle will be pointing toward the north, the other will be pointing toward the south.
Do you know why this happens?
It happens because the earth is a huge magnet. The earth has a north magnetic pole and a south magnetic pole. The magnetism in these poles is very strong. It is strong enough to pull on your compass needle and make it point in a north and south direction.
If you have a globe that is round like a ball, you may find a north and south pole marked on it. These poles are the geographic North and South Poles. The magnetic poles of the earth are near these Poles. But how can you tell which end of your compass needle is pointing to the magnetic north, and which pointing to the south magnetic pole? There is more than one way to discover this. One easy way is to use a regular compass like the one pictured here. Set it down flat on the table near your homemade compass.
The end of the compass needle that points north is usually dark-colored. The end of your needle that points in the same direction as the dark-colored end of the other compass is pointing north. Of course, the other end is pointing south. If you face toward the north, then east will be toward your right and west will be toward your left.
There are other ways besides the compass to tell which way is north. Can you think of some?