The laws list
N
 26Lw14 Laws
NA to null experiment.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
N.
NA
NL
See Loschmidt constant.
negative feedback principle
The idea that in a system where there are self-propagating circumstances, those new circumstances tend to act against previously existing circumstances. Such a principle is really a restatement of a conservation law.

Example Lenz's law.

newton; N (after Sir I. Newton, 1642-1727)
The derived SI unit of force, defined as the force required to give a mass of 1 kg an acceleration of 1 m/s2; it thus has units of kg m/s2.
Newton's law of universal gravitation (Sir I. Newton)
Two bodies attract each other with equal and opposite forces; the magnitude of this force is proportional to the product of the two masses and is also proportional to the inverse square of the distance between the centers of mass of the two bodies; mathematically,
F = (G m M/r2) e,
where m and M are the masses of the two bodies, r is the distance between. the two, and e is a unit vector directed from the test mass to the second.
Newton's laws of motion (Sir I. Newton)
Newton's first law of motion
A body continues in its state of constant velocity (which may be zero) unless it is acted upon by an external force.
Newton's second law of motion
For an unbalanced force acting on a body, the acceleration produced is proportional to the force impressed; the constant of proportionality is the inertial mass of the body.
Newton's third law of motion
In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction force.
Noether theorem (Noether)
A theorem which demonstrates that symmetries are what gives rise to conserved quantities. For instance, translational symmetry (the fact that the laws of physics work the same in all places) gives rise to conservation of momentum, since position and momentum are complementary. Additionally, conservation of energy is indicated by time symmetry, and conservation of angular momentum is indicated by isotropy.
no-hair conjecture (1960s)
The conjecture (proved in the 1970s and 1980s) within general relativity that a black hole has only three salient external characteristics: mass, angular momentum, and electric charge. All other properties (including baryon number, lepton number, strangeness, etc.) are destroyed as matter falls into the horizon.

Note that there is some indication that quantum mechanical considerations in quantum gravity will result in a "quantum hair" coming into play. However, that 1. would constitute a prediction of a theory which does not yet formally exist, and 2. is utterly insignificant for solar-massed black holes, the only types that can be formed today.

null experiment
An experiment which, after being executed, yields no result. Null experiments are just as meaningful as non-null experiments; if current theory predicts an observable effect (or predicts there should be no observable effect), and experimentation (within the required accuracy) does not yield said effect, then the null experiment has told us something about our theory.
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