Magnetism and Energy

In this lesson, students explore the phenomena of how magnets can exert a force on other magnets and magnetic materials without coming into contact with each other. They first investigate the relationship between the number of magnets in a system and the size of the magnetic field produced, and then investigate how the amount of potential energy stored within a system of interacting magnets can change when the distance between the magnets changes.

• Magnets are objects that produce a magnetic field. A magnetic field is the invisible area around a magnet that attracts or repels other magnets and magnetic materials such as iron.
• All magnets have a north pole and a south pole. The north pole of one magnet always attracts the south pole of another. However, two north poles will always repel each other. Two south poles will also repel each other. The interactions of the two magnets depend on how each one is oriented relative to the other.
• A system of interacting objects can store different amounts of potential energy. Whenever objects interact, they form a system that energy can be transferred into or out of.
• Energy can be transferred into a system by a force, and the amount of energy a system can store depends on the amount of force applied to the system.

• How do you know that magnets can exert a force on other magnets without coming into contact with them?
• Why do magnets sometimes attract each other and sometimes repel each other?
• How do the principles of magnetism explain how refrigerator magnets work?
• Where does gravitational potential energy come from?
• Why do two magnets form a system?
• How can you apply a force to the system of magnets?
• How do you think the application of force, either pushing or pulling, would affect the energy of the system of interacting magnets?

Misconception: All metals are attracted to magnets. 

Fact: Metals attract some metals, including iron, nickel, and cobalt. However, many metals, including copper, silver, and gold, are not attracted to magnets.

Attract : to pull toward

Magnet : an object that produces a magnetic field

Magnetic field : the invisible area around a magnet that attracts or repels other magnets and magnetic materials such as iron

Repel : to push away

Navigating by Earth’s Magnetic Field

Dorothee Kremers is a scientist. She and a team of scientists were curious if bottle-nosed dolphins are able to sense magnets. Magnets are objects that produce a magnetic field. A magnetic field is the invisible area around a magnet that attracts or repels other magnets and magnetic materials such as iron.

Earth – A Giant Magnet

The reason scientists care about animals’ ability to sense magnetic fields is that Earth itself is a giant magnet. It has a magnetic field that is created in Earth’s liquid iron core and extends far into space. Scientists believe animals such as dolphins, sea turtles, bats, spiny lobsters, and many insects navigate from place to place using Earth’s magnetic field.

Understanding how Earth’s magnetic field could help animals navigate begins with the basic rules of magnetism. Magnets exert a force on other magnets or magnetic materials. A force is a push or pull that acts on an object, changing its speed, direction, or shape. Magnets either repel or attract other magnets or magnetic materials. To repel means to push away. To attract means to pull toward.

All magnets, including Earth itself, have a north pole and a south pole. (Earth’s magnetic north pole is actually near the South Pole, while its magnetic south pole is near the North Pole.) The north pole of one magnet always attracts the south pole of another. However, two north poles will always repel each other. Two south poles will also repel each other.

Magnetic Fields

One hypothesis about how animals navigate using Earth’s magnetic field is that they have tiny magnetic particles in their cells that react with Earth’s magnetic field, somehow signaling the nervous system in a way that guides the animals as they travel around the planet.

However, scientists cannot say for sure how animals use Earth’s magnetic field. The scientists who studied dolphins focused on one part of this question: Can dolphins sense magnets?

Dolphins Sense Magnets

Dorothee and her team set up an experiment with six dolphins. They set up two different kinds of barrels. One kind of barrel was made of a magnetic material. The other kind of barrel had an identical shape and density, but it was demagnetized. The scientists then videoed how the dolphins interacted with the different barrels. Their experiment showed that the dolphins swam toward the magnetized block much faster than they swam toward the demagnetized block.

The scientists still don’t know exactly how animals can sense magnetic fields. But they believe that animals in the ocean may benefit from having a magnetic sense that detects Earth's magnetic field. This is because the ocean is vast, with few landmarks that animals can use to mark their path. “Inside the ocean, the magnetic field would be a very good cue to navigate," Dorothee said in a 2014 interview with Live Science.

The experiment didn’t tell scientists that dolphins could sense Earth’s magnetic field. This is because the magnets used by the scientists had a much stronger magnetic field than Earth’s own magnetic field. More research needs to be done to explore whether dolphins can sense Earth’s weaker magnetic field, and if this is how dolphins navigate.

For the main hands-on activity of this lesson, students first create a model to explore the size of a magnetic field phenomena and then carry out an investigation to evaluate how the amount of potential energy stored in a system of repelling magnets can change depending on the position and configuration of the magnets. Students use their investigations to figure out how magnets are able to exert the phenomena of force on other magnets or magnetic materials without coming into contact with each other and how a system of interacting magnets can store different amounts of potential energy.