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The strong force keeps also the protons together in the nucleus, despite their mutual electrostatic repulsion.
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The Nuclear Force

The protons in the nucleus of an atom are positively charged. If protons interact, they are usually repelled (pushed apart) by the electromagnetic force. However, when two or more nuclei come very close together (on the order of 1 femto-meter (fm) =10-15 meters), their interaction becomes dominated by another force, the nuclear force, whose intensity is much higher (about 100 times) than the electromagnetic (repulsive) force.

The nuclear force is also known as the strong force or the color force. This is one of the four fundamental forces that govern all the interactions in the Universe.

The nuclear force keeps together the most fundamental of elementary particles known, the quarks, which combine to form the protons and neutrons in the atomic nucleus. The nuclear force also keeps the protons together in the nucleus, despite their mutual electrostatic repulsion. Beyond the distance of 1 fm the nuclear force decreases sharply, becoming practically negligible.


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