# what is magnetism? Can an object increase/decrease in magnetism?

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what is magnetism? Can an object increase/decrease in magnetism?

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Magnetism is interesting phenomenon. It is an aspect of the electro-magnetic force. You can change the magetic field of an object. An electro-magnet is one example of this. Allow a current to flow through the coil and you have a magnet. Remove the current and magnetism goes away (for the most part anyways).

Even more interesting is that you change the magnetic field of an object just by running past it. A moving electric charge creates a magnetic field. Let’s put a negative static charge on a ball. Standing next to the ball you will only be able to detect an electric field.

Now suppose someone else drives by the ball in a car. If they had a sensitive enough measurement device, then the guy driving by in a car would detect a magnetic field created by the ball (they’d also sense the electric field). The faster they go the stronger the magnetic field they detect. You, still standing next to the ball when they drive past, will still only be able to measure an electric field–no magnetic field. Fun!

Magnetism is what you get when electric charges *move*.

So if you run an electric current through a wire, you get a magnetic field. And, if you *change* the magnetic field passing near a wire, that can cause an electric current to start up. That’s the basis of a solid majority of our electrical power generation and transmission: Fuel generates heat, that boils water to get steam, that turns a turbine, that moves strong magnets near wires, that causes an electric current, which can be directed to people’s homes to give us all electrical power. Every electric motor also uses this feature of magnetism.

So, magnetism is what you get when electric charges move. And every single electron in the world is, in a weird sense, “moving”, spinning on some axis, so it has a little magnetic field. On most materials, all these tiny magnetic fields cancel out, but in some (eg, iron), they might not. Iron can be “magnetised” by arranging for (many of) the tiny magnetic fields of the individual atoms to line up and point in the same direction.

And yes, it’s possible to increase or decrease the strength of magnetised iron (or other magnetic materials)

* get a pin or needle (one made of steel), and stroke it with a magnet several times in the same direction – the pin or needle will then become a little magnet, and if you float it on water somehow it will turn to line up with the earth’s magnetic field. Here, the magnetic field you apply induces the mini-magnets within the steel to line up.
* get a magnet, and heat it up enough, and when it cools down, it won’t work as a magnet any more. Here, the heat scrambles the min-magnets in the metal, so they don’t line up any more.

This was, once, the basis of a huge percent of our sound recording industry – a strip of tape coated with very fine iron particles could be “magnetised” with a pattern that represented the sound (or other information) you wanted to record, by imposing a strong magnetic field onto the tape as it rolled by. Then, rolling it by a special device (the “read head”), the tiny magnetic “charges” would induce electric currents in the read head, that would be amplified back to generate the sound.