NATURAL FORCE FIELDS
The North Pole has always been in the north. Or has it? Students will investigate magnetic fields using bar magnets and model the Earth's magnetic field to determine which way is north, and why.
To allow students to see that magnetic fields exist and how they apply to the world.
Students will be able to:
- Describe with an original illustration what a magnetic field looks like
- Model the Earth's magnetic field and illustrate it
Activity: 30 min.
Bar magnets Iron filings Clear plastic bag Staples Overhead projector (variation on white poster board)
Earth's core is a large magnet. It is the source of the planet's magnetic field. Molecules of metal comprising the core are all aligned in the same direction. This alignment causes the poles of the natural magnet of the core to form.
If you stroke a needle with a strong magnet the molecules in the needle temporarily align the same way causing the needle to become magnetized. When the needle is suspended from a string it will align with Earth's magnetic pole.
Due to the size of Earth's core, the magnetic field it produces affects all smaller magnetic fields and tries to align the smaller fields with the larger one. When lava oozes out of the crust, molecules are randomly aligned. As it cools and solidifies, molecules begin to align with the current north. Along the Mid-Atlantic ridge in the Atlantic Ocean, basalt deposits record magnetic flips of the poles. Throughout Earth's history the poles have actually reversed many times. At those times if you were holding a compass, the needle would point south instead of north. The pole switch is a result of the core being surrounded by a liquid. Because of the inner cores independence from and other solid surface it can change or reorient itself easily. Scientists know that this has happened by studying the rock record.
True magnetic north is not the same as geographic north. This is because the core acts independently from the Earth's rotation and it is the axis of this rotation that determines geographic north. The difference between the geographic and magnetic poles is called declination. Declination changes slightly from year to year sometimes only by a few feet, other times by a huge distance.
If you were going to draw a magnetic field, you could draw lines coming out the North Pole and circling back around and entering the South Pole. This demonstration will create those lines of force in a way that students can observe and illustrate.
- Put the bar magnet into a clear plastic zipper bag; this will allow for easier cleanup. Place the magnet and the bag together on an overhead projector and turn on the projector. It should throw a shadow of the magnet up onto the wall.
- Ask the students what kinds of things we know would stick to this magnet. Based on the list that they provide, ask them to predict what would happen if we sprinkled these little pieces of iron onto the magnet. Would they all stick to the magnet, all over it, or would some places on the magnet hold more of the iron pieces than other places?
- Write their predictions on the board.
- Sprinkle iron filings onto the overhead around the magnet in the bag.
- On a piece of paper or in their science journals, have the students draw what they are observing. The lines that the iron filings are making are formed along lines of pull. This is called the magnetic field.
- Discuss what the magnetic field looks like and hypothesize what the field of different types of magnets would look like.
- Try other types of magnets: horseshoe magnets, neodymium magnets, refrigerator magnets, whatever you have available.
What does the magnetic field around this magnet look like? If we used a different magnet, what would the field look like? Try this experiment with another type of magnet, and repeat.
Considering that the Earth is a huge magnet, what does the magnetic field around the Earth look like? Hypothesize what the Earth's magnetic field looks like by drawing onto a page of paper or in their science journals.
If you do not have access to an overhead projector, the same experiment can be done by placing shavings onto a white piece of paper and placing the magnet, (in a clear plastic bag) on top of that piece of paper. You could also have the students observe the relative strength of each magnet.
Included National Parks and other sites:
Utah Science Core:
Kindergarten Standard 4 Objective 1
5th Grade Standard 3 Objective 1, 2