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The orbital motions of planets and comets, as depicted here, are governed by the laws of mechanics.
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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.

Last modified September 12, 2008 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF