3 - 5
15 min - 1 hr
Could you find your home using only earth’s magnetic field?
If you suddenly found yourself lost, hundreds of miles from your home and in a new place, do you think you would be able to find your way back on your own? What if you didn’t have a cell phone or map, and it was nighttime? Don’t feel too bad if you think you’d be permanently lost. Compared to other members of the animal kingdom, humans are terrible navigators. Throughout our long history as global travelers, we have relied on a variety of tools, like compasses and GPS, to help us find our way. Surprisingly, many species of animal are capable of navigating around the world—even at night and underwater—without any devices to help them!
Sea turtles are one of these extraordinary examples. After sea turtles hatch on a beach, they promptly crawl into the water where they spend their juvenile life traveling within and across entire oceans. When they are ready to reproduce after many years at sea, sea turtles are able to find their way back to the same beach where they were born. This ability isn’t unique to sea turtles, either. Pigeons, lobsters, and honeybees can find their way home, too. But how do they do it?
After many years of research, scientists studying migratory species in the lab and in the field eventually noticed that some of the world’s greatest animal navigators have one thing in common: they can detect magnetic fields.
All around the surface of the earth there is a magnetic field generated by the earth’s large magnetic core. The magnetic field varies in strength and direction from place to place and over time, giving different locations unique magnetic “maps.”
If you wanted to detect earth’s magnetic field, you would probably need a compass. A compass is just a small magnet that is allowed to rotate and respond to another more powerful magnetic field. By observing the orientation of a compass, humans can learn the direction of earth’s magnetic field almost anywhere on the planet.
But animals like sea turtles and homing pigeons don’t need a compass. They are able to detect not only the direction, but also the strength of a magnetic field without any help at all. By detecting natural magnetic fields around them, animals like these are able to identify their location and navigate to a familiar place, a behavior called magnetic homing. You can learn more about magnetic homing in sea turtles in this SciFri interview:
How can you navigate like a sea turtle? Find out by making a turtle that can detect magnetic fields, creating your own magnetic map, and playing a game to find your turtle’s habitat.
- Cereal box
- 5-10 refrigerator magnets of varying strengths*
*Careful – strong magnets can ruin electronics and credit cards that they come into contact with
- Bolt, screw, or nail that is ferromagnetic (sticks to magnets)
- Modeling clay or play dough (DIY recipe here)
Make a Turtle Navigator:
- Tie a string to a nail or bolt
- Press a small amount of modeling clay or play dough onto your bolt, pulling the string so that it comes out of the top. Carefully sculpt a turtle out of the clay, making sure to keep the bolt on the bottom and the string on the top. Test your turtle to make sure that it hangs easily when you hold it by the string, and adjust as needed. It should look like this when you’re done:
- Practice holding your turtle by the string and moving it carefully over one of the refrigerator magnets. Watch how it moves when it gets close to, and touches the magnet.
Make a Magnetic Map:
On your own or with the help of an adult, cut a cereal box in half long ways, and tape the corners of one half so it holds its shape when it is set on a table. Trim the edges of the box so that the surface sits about one inch from the table, like this:
- Place a few magnets on a desk or table and cover them up with the box. Tape the sides of the box to the table to hold it in place. This is your turtle habitat.
- Use your markers to label a plain piece of paper “magnetic map.” You can also give it a beach or ocean name if you’d like. Tape the piece of paper onto the top of the box.
- Holding its string, slowly suspend your turtle above the turtle habitat, moving it back and forth until you notice it move in response to one of the magnets.
- Draw a small dot or circle where you think a magnet is.
- Next, slowly move your turtle around the magnet you just found, noting how far away you can get and still detect the magnetic field of the magnet by the movement of your turtle. Draw a circle around the entire area where your turtle can detect the magnet.
- Continue searching for, marking, and circling the magnetic fields until you have recorded the location and magnetic field sizes of all the magnets in your turtle’s habitat. You’ve created a magnetic map!
- When you think you have finished, carefully remove the tape holding the turtle habitat to the table, and lift the turtle habitat up to look at the magnet positions. Compare your map to the positions of the magnet. How similar are they?
Turtle Navigation Game (for 3-6 players)
- Cut three cereal boxes in half long ways and tape the corners of all six half-boxes so they hold their shape.
- Print out these six magnetic field maps—each shows the position of magnetic field sources in a different turtle habitat—along with the map key.
- Have one person use the map key to recreate the six different habitats, doing their best to replicate the number, relative size, and location of each magnet. Once they finish, cover each habitat with a half of a cereal box and tape the sides of each box to the table to hold it in place. (The other players should not watch these steps.)
- Make sure every player has a navigator turtle and has practiced using it with a magnetic map (activity above).
- Pass out one magnetic map to each player, and then start the search for matching habitats! Each player can use only their turtle to explore the habitats, and must keep exploring until they find the one that they think matches their magnetic map.
- When all players think they have found the habitat that matches their map, count to three, and then all at once lift off the boxes to see who’s correct.
Next Generation Science Standards:
- 3-PS2-4 Define a simple design problem that can be solved by applying scientific ideas about magnets
- MS-PS2-3 Ask questions about data to determine the factors that affect the strength of electric and magnetic forces
- 4-LS1-2 Use a model to describe that animals receive different types of information through their senses, process the information in their brain, and respond to the information in different ways