The laws list
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N_{A} to null experiment.


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N.

 N_{A}

See Avogadro constant.
 N_{L}

See Loschmidt constant.
 negative feedback principle

The idea that in a system where there are selfpropagating
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, 16421727)

The derived SI unit of force, defined as the force required to
give a mass of 1 kg an acceleration of 1 m/s^{2}; it thus has units
of kg m/s^{2}.
 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/r^{2}) 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.
 nohair 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 solarmassed 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 nonnull 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.
See MichelsonMorley experiment.

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