Similarities Between Gravity and Magnetics
Geophysical investigations employing observations of the earth's magnetic field have much in
common with those employing observations of the earth's gravitational field. Thus, you will find
that your previous exposure to, and the intuitive understanding you developed from using,
gravity will greatly assist you in understanding the use of magnetics. In particular, some of the
most striking similarities between the two methods include:
- Geophysical exploration techniques that employ both gravity and magnetics are passive.
By this, we simply mean that when using these two methods we measure a naturally occurring field
of the earth: either the earth's gravitational or magnetic fields. Collectively, the gravity and
magnetics methods are often referred to as potential methods*, and the gravitational and
magnetic fields that we measure are referred to as potential fields.
- Identical physical and mathematical representations can be used to
understand magnetic and gravitational forces. For example, the fundamental element used to define
the gravitational force is the point mass.
An equivalent representation
is used to define the force derived from the fundamental magnetic element.
Instead of being called a point mass, however, the fundamental magnetic element is called a
magnetic monopole.
Mathematical representations for
the point mass and the magnetic monopole are identical.
- The acquisition, reduction, and interpretation of gravity and magnetic observations are very
similar.
*The expression potential field refers to a mathematical property of these types of force
fields. Both gravitational and the magnetic forces are known as conservative forces. This
property relates to work being path independent. That is, it takes the same amount of work to
move a mass, in some external gravitational field, from one point to another regardless of the path
taken between the two points. Conservative forces can be represented mathematically by simple
scalar expressions known as potentials. Hence, the expression potential field.
