sat物理常用术语词汇：N

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Neutrino

An almost massless particle of neutral charge that is released along with a beta particle in beta decay.

Neutron

A neutrally charged particle that, along with protons, constitutes the nucleus of an atom.

Neutron number

The number, N, of neutrons in an atomic nucleus.

Newton

A unit of force: 1 N is equivalent to a 1 kg • m/s2.

Newton’s First Law

An object at rest remains at rest, unless acted upon by a net force. An object in motion remains in motion, unless acted upon by a net force.

Newton’s Law of Universal Gravitation

The force of gravity, F, between two particles of mass and , separated by a distance r, has a magnitude of , where G is the gravitational constant. The force is directed along the line joining the two particles.

Newton’s Second Law

F = ma. The net force, F, acting on an object causes the object to accelerate, a. The magnitude of the acceleration is directly proportional to the net force on the object and inversely　proportional to the mass, m, of the object.

Newton’s Third Law

To every action, there is an equal and opposite reaction. If an object A exerts a force on another object B, B will exert on A a force equal in magnitude and opposite in direction to the force exerted by A.

Node

The points on a standing wave where total destructive interference causes the medium to remain fixed at its equilibrium position.

Normal

The line perpendicular to a surface. There is only one normal for any given surface.

Normal force

The reaction force of the ground, a table, etc., when an object is placed upon it. The normal force is a direct consequence of Newton’s Third Law: when an object is placed on the ground, the ground pushes back with the same force that it is pushed upon. As a result, the net force of an object on the ground is zero, and the object does not move.

Nuclear fission

A nuclear reaction in which a high-energy neutron bombards a heavy, unstable atomic nucleus, causing it to split into two smaller nuclei, and releasing some neutrons and a vast amount of energy at the same time.

Nuclear fusion

A nuclear reaction that takes place only at very high temperatures. Two light atoms, often hydrogen, fuse together to form a larger single atom, releasing a vast amount of energy in the process.

Nucleus

The center of an atom, where the protons and neutrons reside. Electrons then orbit this nucleus.

小编提醒：单词的记忆要靠长期的坚持，考生们一定要持之以恒，每天都拿出来看一看背一背，让这些词汇在大脑中形成长期记忆，这样就不会轻易地忘记背过的词汇了。