Junior high students should understand the influence of atmospheric conditions on natural forces. This concept is demonstrated in an experiment designed to establish the relationship between a magnet's temperature and its external force. Place five identical horseshoe magnets in a freezer overnight to stabilize all the subjects at 0 degrees Celsius. Spread 100 washers out on a flat surface and run each magnet over the surface to confirm magnetic force is uniform among all magnets and return them to the freezer. Place one magnet on a burner in water heated to 25 degrees Celsius for 10 minutes. Remove the magnet and run it over the washers. Record the number of washers attracted. Repeat the process, moving magnets directly from the freezer to the burner in water heated to 50, 75 and 100 degrees Celsius. Run the last magnet over the washers immediately after removing from the freezer. Based on the data, it should be concluded that increasing temperature decreases a magnet's pull.
While all naturally occurring elements are composed of some magnetic components, some are present in such small concentrations they appear to possess no attraction. Science teachers should discuss magnetic properties as an attribute commonly used to identify and classify elements. Create a list of common items, including coins, sand, batteries, salt and metal jewelry. Ask students to hypothesize which objects are attracted by magnets. Test theories by providing a magnet to each child and a row of samples of each item listed on the board.
Junior high science teachers can add an interesting twist on an elementary concept in an experiment about opposite poles. Give each student a magnet with north and south poles labeled and an unmarked magnet. Discuss the fact that opposite poles are attracted to one another, while the same poles repel. Ask students to identify north and south poles of the unmarked magnet by placing it near the labeled magnet and applying the "opposites attract" rule. Assign students a partner and give each pair 10 large ring magnets and an upright paper towel holder. Instruct pairs to determine which ring sides repel each other and drop two onto the paper towel rod with the same poles facing each other. Students should record their observations. Continue adding magnets with like poles facing until all 10 are on the rod. Ask students to predict what will happen if all the magnets are compressed on one another and released. Pairs should test their hypothesis by pressing down on the magnets with one hand until they are all touching before quickly moving the hand away.
Most junior high students should be familiar with the idea that gravitational force exerts the same pull on any object on earth, regardless of its weight. Teachers can review this concept by dropping two items of different weight, such as an apple and paper wad, from a desk. They will hit the floor at the same moment. Discuss factors that interfere with gravitational pull, such as wind resistance, which will cause a sheet of paper to drop at a slower rate than a paper wad, and magnetic field interference. Present a copper pipe 36 to 48 inches in length, a heavy magnet that will fit easily in the tube, and a steel ball the same weight as the magnet. Drop the magnet and ball to show they will hit the ground at the same time. Repeat the experiment, but drop the magnet through the copper tube, which should be held 12 inches above the ground. Students will see that the attractive force the copper distributes over the magnet will slow its path, and the steel ball will reach the ground first.