Remember, there are four different kinds of forces: strong nuclear force,
electromagnetism, weak nuclear force, and gravity. There are also four basic force fields that you come into contact with all the time. They are the gravitational field, the electric field, the magnetic field, and the electromagnetic field. Notice that those four force fields really only use two of the four different kinds of force: electromagnetism and gravity. Let’s take a quick look at what causes these four fields and what kind of objects they can affect, starting with the magnetic field.
Here’s what you need:
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- you
- a compass
You’re probably fairly familiar with magnetic fields. If you’ve ever stuck a magnet to a refrigerator, you’ve taken advantage of magnetic fields. Sticking a magnet to a refrigerator is one of those every day experiences that should just be absolutely flabbergasting. There you are holding an “I’d Rather be Relative” magnet and it sticks to the fridge! But wait a minute, if you put it on the wall… it falls off! How does it “know” what to stick to? Not only does it stick to the fridge, it also pushes some things away, attracts other things and couldn’t care less about still other things. What’s that all about?! We rarely think about what magnets do but, wow, the things they do are weird!
Magnetic fields come from objects that have a surplus of electrons all moving in the same direction. This can be an electric wire with current running through it or one of several special types of metals. Iron, nickel and cobalt are the most common metals that can be magnetic. Magnetic fields can only affect objects that can be magnetic themselves. That’s why a magnet can attract an iron nail, but it can’t attract an aluminum can. The iron nail can be magnetic, but the aluminum cannot. Magnets can also be attractive or repulsive. Two magnets with the same kind of poles facing one another will push themselves apart. Two magnets with opposite poles facing one another will pull themselves together.
Download Student Worksheet & Exercises
Using a compass and the Earth, you can do a simple experiment to detect the magnetic field of our planet. (If you don’t have a compass, just slide a magnet along the length of a needle several times (make sure you only swipe in one direction!) then stick it through a cork or bit of foam. Float the needle-foam thing in a cup of water.)
1. Look at the compass
2. Walk anywhere and keep your eye on the compass.
3. Turn around in circles and keep your eye on the compass (don’t get too dizzy).
Again a very simple little activity, but I hope you can see the point. No matter where you went or what you did, that needle always pointed the same direction! The Earth’s magnetic force field, another strange and mysterious force, always pushes that needle in the same direction. It’s invisible and you can’t feel it…but the needle can!
Exercises
- Why does the needle need the foam?
- Why do we use water?
- What are the forces in a magnetic field?
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