Discovering the Magnetic Force

Learning Objectives

The goal of this activity is for students to understand the basic properties of the magnetic force. They should understand that it works at a distance and acts mostly on metals.

Materials

• 1 or 2 magnets
• Shoe box
• String
• Playdough
• Paper clips or ball bearings (or both), pennies, nickels, and dimes (maybe 2 of each)
• Plastic cubes, chunks of wood, or other small non-metal objects (for contrast)
• Ruler
• Wool
• Small dish
• Water
• Sewing needle
• Small piece of paper (only needs to be big enough to hold the needle)

Motivation

The magnetic force is one of the most fundamental interactions in our universe. Every magnet has two poles, north and south. Magnets interact with each other under one rule: like poles repel and opposite poles attract. Magnetic metal objects (like coins, or paper clips) are always attracted to magnets. Even though it is mostly metals that are attracted to magnets, not all metals are magnetic. Aluminum, for example, will not be attracted by a magnet. Magnets produce magnetic fields, which are a source of attraction for magnetic objects. The earth is one giant magnet, and produces a magnetic field just the same as small magnets do. The arrow on a compass is magnetized, and aligns with Earth’s magnetic field such that it always points north.

Part 1 is a demonstration of how the magnetic force acts at a distance. Depending on how strong your magnet is, the paper clip could react from very far away, or it might not react until the magnet is close. The magnetic force is very interesting because, in general, it only acts on metals. In Part 2, by placing a variety of different objects on the cardboard, the student should be able to recognize that only the metal objects are affected by moving the magnet around underneath the cardboard, and that non-metal ones are not affected.

Finally in Part 3, we will build a very simple compass. This will demonstrate that the earth generates a magnetic field. If you have a compass available to you, you can double check that the needle does indeed point north.

Procedure

Part 1

Tie a paper clip to a piece of string, and dangle it from something (the edge of a desk works well). Slowly bring a magnet closer and closer and see what happens. Using a ruler, estimate the distance required for the paper clip to react.

Part 2

Cut a hole in the side of your shoe box and leave the bottom open. Use some Playdough, if available, to build a barrier at the edge of your box so objects won’t fall off the top. Place paper clips, pieces of paper, plastic cubes, or other small objects on top of the cardboard. With the magnet between your fingers, move it around underneath the cardboard, watching on top. Make note on the worksheet of which objects move.

Part 3

Fill a small dish or cup with water, not quite to the top. Carefully rub the sewing needle in the wool, and place it on the paper. Then, very gently, lower the paper into the water. As the paper floats, it will begin to rotate, and eventually point north. Once it has stopped rotating, give it a gentle nudge, and watch it return to the position it was just in!

Investigating Questions

• Is the magnetic force an impact force, or a force at a distance?
• What does the magnetic force act on?
• What produces a magnetic field?
• How does a compass work?
• The Earth has a _______________________________, just like a magnet.