62: Special Relativity
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The classical mechanics described by Sir Isaac Newton begins to break down at very high velocities, i.e. at velocities near the speed of light c=299,792.458 km/s. For bodies moving at a significant fraction of the speed of light, Newton's mechanics needs to be modified. The necessary modifications were developed by physicist Albert Einstein in the early 20th century, in a theory now called the special theory of relativity.