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Undoubtedly the most famous equation ever written is E=mc^2. This equation says that energy is equal to the rest mass of the object times the speed of light squared (c is universally accepted as the speed of light). What is this equation actually telling us? Mathematically, since the speed of light is constant, an increase or decrease in the system's rest mass is proportional to an increase or decrease in the system's energy. If this relationship is then combined with the law of conservation of energy and the law of conservation of mass, an equivalence can be formed. This equivalence results in one law for the conservation of energy and mass. Let's now take a look at a couple examples of this relationship...
You should readily understand how a system with very little mass has the potential to release a phenomenal amount of energy (in E=mc^2, c^2 is an enormous number). In nuclear fission, an atom splits to form two more atoms. At the same time, a neutron is released. The sum of the new atoms' masses and the neutron's mass are less than the mass of the initial atom. Where did the missing mass go? It was released in the form of heat - kinetic energy. This energy is exactly what Einstein's E=mc^2 predicts. Another nuclear event that corresponds with Einstein's equation is fusion. Fusion occurs when lightweight atoms are subjected to extremely high temperatures. The temperatures allow the atoms to fuse together to form a heavier atom. Hydrogen fusing into helium is a typical example. What is critical is the fact that the mass of the new atom is less than the sum of the lighter atoms' masses. As with fission, the "missing" mass is released in the form of heat - kinetic energy.
One often-misinterpreted aspect of the energy-mass unification is that a system's mass increases as the system approaches the speed of light. This is not correct. Let's assume that a rocket ship is streaking through space. The following occurs:
In step 2, the system's resistance to acceleration is a measurement of the system's energy and momentum. Take notice that in the above 4 steps, there is no reference to mass. Nor does there need to be.
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