Magnetic forces are produced by the motion of charged particles
such as electrons, showing the close relationship between magnetism and electricity.
The most familiar form of magnetism is the attractive or repulsive force that acts between
magnetic materials such as iron. Other effects of magnetism, however, are found in all objects.
Magnetic fields are described in terms of their effect on electric charges. A moving electric
charge will accelerate or speed up in the presence of a magnetic field, causing it to change
speed or velocity and i's direction of travel.
The north pole of a magnet is the pole that aligns itself with geographic north. As a result,
the geographic north pole of the earth is actually very near the earth's magnetic south pole.
The strength of a magnetic field is measured in units of Gauss(G), or alternatively, in Tesla(T).
In the metric system of units, 1 T=1 kilogram* ampere/second^2=10^ 4G. The magnetic field of
the earth at the surface is on the order of 1 Gauss, where that of a Neodymium magnet is on the
order of 10^4 Gauss. This means that Neodymium magnets produce magnetic fields tons of thousands
of times stronger than the ones of the Earth.
The strength of a magnetic field at a given distance from a magnet is approximately proportional
to the universe cube of the distance from the magnet. Therefore, if you double the distance
from the magnet, the magnetic field strength is reduced by about a factor of eight.