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The goal of physics is to provide an understanding of the physical world by developing theories
based on experiments. A physical theory is essentially a guess, usually expressed mathematically,
about how a given physical system works. The theory makes certain predictions
about the physical system which can then be checked by observations and experiments. If the
predictions turn out to correspond closely to what is actually observed, then the theory
stands, although it remains provisional. No theory to date has given a complete description of
all physical phenomena, even within a given subdiscipline of physics. Every theory is a work in
progress.
The basic laws of physics involve such physical quantities as force, velocity, volume, and
acceleration, all of which can be described in terms of more fundamental quantities. In mechanics,
the three most fundamental quantities are length (L), mass (M), and time (T); all
other physical quantities can be constructed from these three.

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