what gives earth its magnetic Field?
There are many web pages with tips for what to look for when buying a used motorcycle. Google the phrase buying a used motorcycle (with quotes) and you'll see. If it was me, I'd want to bring someone along to test-ride the bike, because there are things you will only notice that way. I've done this for a few of my friends who were buying their first bike.
Your best bet is to find someone who does know how to ride (and is mechanically inclined) to come along and take a look at it with you. I usually suggest an old beat-up dirt bike for a first motorcycle - that way when (not if) you drop it, you don't scuff up a nice new one.
The field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated spins of electrons and nuclei within iron atoms. The Earth's core, however, is hotter than 1043 K, the Curie point temperature at which the orientations of spins within iron become randomized. Such randomization causes the substance to lose its magnetic field. Therefore the Earth's magnetic field is caused not by magnetized iron deposits, but mostly by electric currents in the liquid outer core (as it spins, electrons tend to stay behind, thus producing a small current). Another feature that distinguishes the Earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field. Electric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations which can deflect surface magnetic fields by as much as one degree.
Geomagnetic fields are reasonably complicated, but the basic idea behind Earth's field has to do with the interactions in its core, resulting in a geomagnetic dynamo. The Earth's core, which is mostly iron and nickel, has two parts: a solid inner core and a molten outer core. These materials are magnetic, resulting in small, local magnetic fields inside the material. As the molten outer core sloshes around and rubs against the solid inner core, it passes through the local magnetic fields. This generates an electric current, and electric currents generate magnetic fields. This flowing of liquid metal through a stronger magnetic field generates more current.which causes a stronger magnetic field.which results in more current flowing.etc. So, this is a self-sustaining dynamo effect. But, the rotation of Earth is also crucial to its existence. The rotation causes the poles of the local magnetic fields to sort of align, resulting in a stronger, larger field. Without the spinning, it is likely that the individual fields would mostly cancel each other out and we would have no significant global magnetic field.
