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nuclear fission

Some more information about nuclear fission can be found in the spotlight topic Is the whole the sum of its parts?. The role played in nuclear fission and fusion by Einstein’s famous formula E=mc² is the subject of the spotlight topic From E=mc² to the atomic bomb.

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nucleus

Extremely dense central region of an atom, consisting of protons and neutrons held together by nuclear forces. The number of protons determines what chemical element a nucleus represents. Typical diameter for atomic nuclei are in the region of a quadrillionth of a metre= 10^-15 metres. This makes nuclei about a hundredth of a thousandth as large as atoms.

nuclei (nucleus)

nuclear fission

Processes in which a heavier atomic nucleus splits up into several lighter nuclei. If the initial nucleus is heavy enough, energy is set free in the split. Nuclear fission reactions are used in nuclear reactors to produce electrical energy, and in nuclear weapons to power an energetic explosion. Some more information about nuclear fission can be found in the spotlight topic Is the whole the sum of its parts?. The role played in nuclear fission and fusion by Einstein's famous formula E=mc² is the subject of the spotlight topic From E=mc² to the atomic bomb.

free

In the context of relativity theory, a particle (object, observer...) that is not acted upon by any force except gravity is said to be free or, a bit more specific, to be in free fall. Free test particles play an important role in understanding the structure of general relativity.

fission

See nuclear fission

energy

Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, thermal energy and the energy carried by electromagnetic radiation. Processes that transform one form of energy into another take place in all machines we use in everyday life, from the engine of a subway train (electrical energy into kinetic energy of the train) to an electric blanket (electrical energy into thermal energy). One important consequence of special relativity is that energy and mass are completely equivalent - two different ways to define what is, on closer inspection, one and the same physical quantity. See the keyword equivalence between mass and energy.

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nuclear fission

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