If a magnet is strong enough, it can work through many materials as if they were not even there. You can stick your favorite piece of artwork to the refrigerator with a magnet. How does the magnet work through the paper? If you try to stick a pad of paper to the same refrigerator, it probably will not work. The magnet and the refrigerator are attracted. The magnetic force will go through the paper, but it does weaken the force a little bit. That is why a magnet can hold one piece of paper on your refrigerator, but not the whole pad of paper.
I have found that children are most amazed and intrigued by the concepts and activities below. All the activities are classroom tested, and have been very well received, many labeled "favorites" by the children.
Magnetism through liquids:
Fill empty 20-ounce soda bottles with a variety of liquids such as: water, milk, light Karo syrup, oil, ginger ale, molasses, etc. Then in each bottle, put a few magnetic objects, such as paper clips or thumb tacks. You could also place some pennies or non-magnetic metal objects in the bottles. Replace the cap tightly, and put some masking tape around the cap so it can not be removed. Use a magnet to move the objects around inside the bottles. Question the children as to why they think this works. Also ask them why the objects in the thicker liquids move more slowly than the objects in the water or the milk.
Magnetism though air:
Tie a 10-15 inch piece of string to a large paper clip. Tape the free end of the string to a table or the floor. With a magnet wand, pull the paper clip up until the string it taught. Then slowly pull the magnet wand away from the paper clip. Notice the paperclip does not fall down, it floats. When you pull the magnet wand too far away from the paper clip, it falls. Question the children as to why they think the paper clip stays in the air even when the magnet is not touching it. This activity really requires you to use magnet wands because they are strong magnets and they have a handle, which enables you to control your movements.
(figure available in print form)
Magnetism through paper or cloth:
This is a very simple activity. Provide some magnetic and non-magnetic objects, scrap paper or newspaper and some fabric scraps. Have one child hide an object under a piece of paper or fabric. Another child will try to guess whether the hidden object is magnetic or non-magnetic. After the child guesses, he/she can place a magnet on top of the paper or cloth, and see if the magnet will attract the object. To add interest and variety, include some cardboard as well as fabrics that vary in thickness.
Magnetism through wood:
Try building a structure similar to the one illustrated below. The small circle in the center should be a magnetic object. Hold a magnet below the thin wooden board and move it around. See if the magnet can swing the pendulum. It should!
(figure availalble in print form)
Magnetism through plastic:
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For this you will need either iron shavings, shavings of steel wool or some very small pieces of metal. Then you will need a shallow plastic or cardboard container with a clear top. Put one of the materials listed above inside the container and seal the top. Then begin moving around the materials inside with your magnet wand. Notice you can even pull the items up the side of the container.
Magnetism through other materials:
Try testing other materials such as glass and your finger to see which ones magnets can attract through.