The orbital motions of planets and comets, as depicted here, are governed by the laws of mechanics.
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Windows to the Universe original artwork by Randy Russell.
Mechanics
Mechanics is the term used to refer to one of the main branches of the science
of physics. Mechanics deals with the motion of and the forces that act upon
physical objects.
We need precise terminology to describe the way objects move. Kinematics is
the sub-field within mechanics that supplies this lingo in the form of concepts
like position, velocity, acceleration, and rotation rates. Forces and the motions
they produce, as specified by Newton's Laws of Motion, are within the realm
of the closely related discipline of kinetics.
The abstract concept of energy also plays an important role in the study of
mechanics. We speak of potential energy in situations such as a ball at rest
at the top of a hill, and kinetic energy when that ball is rapidly rolling
along after descending the hill. Conversion of energy from one form to another
is constrained by the Law of Energy Conservation.
The mechanics of individual, solid objects are the simplest to understand,
but mechanics also deals with the more complex motions of loosely linked collections
of particles. Fluid mechanics describes the motions and forces associated with
traditional liquids, such as water. It also delves into the behaviors of other
"fluids",
including gases such as air and the plasma that makes up the atmosphere of
the Sun.
Complex behaviors also arise when objects start spinning or moving along curved
paths instead of along straight lines. Earth orbits the Sun along a nearly
circular path while spinning upon its axis once each day. Rapidly rotating
gyroscopes
stabilize satellites, while electrons and protons spiral downward along Earth's
magnetic field lines to create auroras.
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