This week, we are going to look at a much less spooky form of action at a distance - magnets.
You will need:
An adult helper.
A magnet - the most powerful one you can find. Try to get one with two definite poles, like a bar magnet or a horseshoe magnet. The flat flexible ones don't work as well.
A couple of books roughly the same width as the magnet.
Steel wool. Use the fine type, not the coarse one. Make sure you don't use the type with soap in it or choose a bit without soap.
Rubber gloves
A piece of paper
An old pair of scissors
Vegetable oil or baby oil.
A small bottle or jar, cleaned and dried.
Caution: Steel wool can contain little pieces of steel which can stick into you like splinters. Please have an adult help you and wear the gloves whenever you are handling the steel wool. Do not touch any other part of your body, especially your eyes, until you have taken off the gloves and thoroughly washed your hands. Do not do this activity anywhere drafty or windy.
What to do:
We are going to do this in two stages. For the first stage:
Put the two books flat on the table with the magnet between them.
Lay the paper on top. It should lie flat with the magnet underneath it.
Put the rubber gloves on.
Steel wool normally comes wound up in a roll. Unroll the first few centimetres, so you have a lot of strands all going the same way.
Hold the steel wool over the paper.
Using the scissors, cut across the strands so the last millimetre or so gets cut off and falls to the paper.
Keep cutting away at the steel wool so you get a pile of fine steel particles on the paper. Move the steel wool around so it falls all over the paper.
Cutting the steel wool. The paper it is falling onto has a magnet underneath it.
The pattern I got on the paper. If you roll your mouse over the image it will show the lines of the magnetic field.
What's happening?
You should notice that the steel particles start to form a pattern on the paper. You will probably find that for a short distance around the magnet, all the steel has been attracted to the magnet. Out beyond that, the steel particles seem to fall so they form loops, starting at one pole of the magnet then going out and around to the other pole. If you look closely at the bits of steel near the magnet, you should see that they have still landed in a similar pattern.
The particles of steel are lining up with the magnetic field of the magnet. The magnetic field is the name given to the pattern of magnetic force caused by a magnet. If you imagine putting a tiny magnet somewhere near your magnet, if would feel a force from the north and south pole of the magnet. The forces would add up to make a force in one direction. The direction and strength of the magnetic force at every point make up the magnetic field.
When the bits of steel come near the magnet, they become slightly magnetised, and so they land lined up with the magnetic field in that area.
Sprinkling tiny bits of steel on a piece of paper shows a cross section of the magnetic field. You can also show the magnetic field in three dimensions. Here's how:
Keep the gloves on.
Pick up the paper by the ends and use it to funnel the steel particles into the bottle.
Fill the bottle with oil and put the lid on it.
Take off the gloves, wash you hands and, if necessary, vacuum around where you were cutting up the steel wool.
Now give the bottle a shake so the steel swirls around inside it. If you hold the magnet near the bottle, you should find the bits of steel line up with the magnetic field again. This time, they show the field in three dimensions. As you move the magnet around, the pattern will move in response. If you hold one pole of the magnet near the bottle, you should find the steel particles all point towards it. You can even try putting a couple of magnets near the bottle to see how the two magnetic fields interact.
Pouring the steel into the bottle.
The magnetic field in the bottle. Again, move your mouse over this image and it will show the magnetic field.
Applications
The Earth has a magnetic field as well. A compass works by lining up with the magnetic field of the Earth. The Earth's magnetic field doesn't line up perfectly with the Earth's axis, so compasses don't actually point to the North Pole, but at a spot called the North Magnetic pole. At the moment the North Magnetic Pole is in Canada and it is moving around 15 km per year.
I always used to wonder what a compass would do if you stood on the North Magnetic Pole. You can see from your bottle that the compass would try to point straight down into the Earth.
