Magnetic Merry-Go-Round

How can you make a merry-go-round turn without pushing it?

When the motor is connected and current is flowing, there are positive charges flowing through the magnet. During the activity the direction of current will change. Sometimes it will be flowing down the nail, through the magnet and to the outside edge of the magnet. Sometimes it will flow from the outside edge through to the middle and back up the nail. Either way, the direction of the current flow will be along the radius of the magnet. The magnetic field points from one flat side of the magnet to the other. The only direction that is perpendicular to both the magnetic field and the direction of the current is the direction of the force. This force is so strong that it causes the magnet to turn.

During this activity the students will set up the motor in various configurations and see which way the magnet turns. Apart from the main physics in this activity, there is a little extra piece shown when the nail is hung from the battery. When a strong magnet is attached to certain metals, it makes the metal object magnetic as well. In this case the neodymium magnet is attached to the head of a nail and then the nail itself becomes magnetic. Your students have probably stumbled across this before with paper clips. If they are touching a magnet, they also become magnets and can pick up more paper clips. Because the end of a battery is made of a metal that magnets can stick to, when the magnet is attached to the head of the nail and nail becomes a magnet, it can hang from the end of the battery.

If your students have had a chance to make electromagnets, they may realize that when current is flowing, it creates a magnetic field. In this experiment we are going to see what happens when current flows through a permanent magnet. The magnetic field created by the current is going to get in the way of the magnetic field of the permanent magnet. Because of the two magnetic fields repelling, the motor will turn.

Current is moving charges. Because of Ben Franklin’s convention we always assume it is positive charges moving, even though we really now know it is negatively charged electrons. From now on, we are just going to assume that the positive charges are moving. Thank you, Ben.

The tricky thing about electromagnetism is that charges that are sitting still don’t interact with a magnetic field that isn’t changing. So an electron could happily sit next to a refrigerator magnet forever and feel nothing at all. But electricity starts affecting magnetism and vice versa as soon as one starts changing. This activity will look at what happens when charges move in a magnetic field that is not changing.

The magnetic field is produced by the neodymium magnet so it won’t be changing, but there will be a current produced by a battery which means that charges will be moving. The direction of the force depends on which way the positive charge is moving and which way the magnetic field is going. One interesting thing is that the force the positive charge feels is not in the direction of the magnetic field or of the particle’s motion – it is perpendicular to both.

• Real world connections:
  • The right-hand rule is a method used by physicists to determine the direction. On the Khan Academy page "Right-Hand Rule" scroll down to read the section titled “Magnetic Field Caused by Current in a Wire.” After you read that, use the right-hand rule to determine the direction of the magnetic field in the different setups. Does it match what you expect?
• Suggestions for drawing, illustrating, presenting content in creative ways:
  • Create an escape room in your classroom. Students should work in small groups to answer questions about this topic (magnets and electromagnets), or construct motors in order to receive clues. The first team to get all of the clues and solve the puzzle gets to “escape!”
  • Make an Art Bot
• Engineering and design challenges connected to the content:
  • Have students compete in a motorized boat challenge using these directions.