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Classical mechanics

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Sir_Isaac_Newton_(1643-1727)Classical mechanics is the physics of forces, acting upon bodies. It is often referred to as “Newtonian mechanics” after Newton and his laws of motion. Classical mechanics is subdivided into statics (which deals with objects in equilibrium) and dynamics (which deals with objects in motion).

Classical mechanics produces very accurate results within the domain of everyday experience. It is superseded by relativistic mechanics for systems moving at large velocities near the speed of light, quantum mechanics for systems at small distance scales, and relativistic quantum field theory for systems with both properties. Nevertheless, classical mechanics is still very useful, because (i) it is much simpler and easier to apply than these other theories, and (ii) it has a very large range of approximate validity. Classical mechanics can be used to describe the motion of human-sized objects (such as tops and baseballs), many astronomical objects (such as planets and galaxies), and even certain microscopic objects (such as organic molecules.)

Although classical mechanics is roughly compatible with other “classical” theories such as classical electrodynamics and thermodynamics, there are inconsistencies that were discovered in the late 19th century that can only be resolved by more modern physics. In particular, classical nonrelativistic electrodynamics predicts that the speed of light is a constant relative to an aether medium, a prediction that is difficult to reconcile with classical mechanics and which led to the development of special relativity. When combined with classical thermodynamics, classical mechanics leads to the Gibbs paradox in which entropy is not a well-defined quantity and to the ultraviolet catastrophe in which a blackbody is predicted to emit infinite amounts of energy. The effort at resolving these problems led to the development of quantum mechanics.

History

The Greeks and Aristotle in particular were the first to propose that there are abstract principles governing nature.

One of the first scientists who suggested abstract laws was Galileo Galilei who also performed the famous experiment of dropping two canon balls from the tower of Pisa (The theory, and the practice showed that they both hit the ground at the same time).

Sir Isaac Newton was the first to propose the three laws of motion (the law of inertia, the second law mentioned above, and the law of action and reaction), and to prove that these laws govern both everyday objects and celestial objects.

Newton also developed the calculus which is necessary to perform the mathematical calculations involved in classical mechanics.

After Newton the field became more mathematical and more abstract.

Further Reading

  • Feynman, R., Six Easy Pieces.
  • —, Six Not So Easy Pieces.
  • —, Lectures on Physics.
  • Kleppner, D. and Kolenkow, R. J., An Introduction to Mechanics, McGraw-Hill (1973).

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