In 1906 Einstein utilized the center-of-mass theorem to derive an expression for the inertia of energy and an expression for the center of mass vector. The paper consisted of two parts the first of which was a spring board for the second part. The first part was entitled "A special case" and the second part was entitled the "On the Principle of the Conservation of the Center of the motion of the center of gravity"(adsbygoogle = window.adsbygoogle || []).push({});

I've created a new web page which describes Einstein's derivation. The page also describes one modification given by Antipa in the Am. J. Phys. I've made one slight modification of his arguement by using the principle of the conservation of (relativistic) mass.

This derivation is commonly known referred to as "Einstein's Box"

http://www.geocities.com/physics_world/sr/einsteins_box.htm

Caution: Please don't confuse the center of mass "frame of reference" with the center of mass "vector." Einstein's work as well as Antipa's, mine and anyone else who describes this work of Einstein's pertains to the center of mass *vector*

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# Einstein's Box

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