SAT2考试时间为一小时，大部分为选择题，主要考察学生某一专业的知识，每科满分为800分，学生可以根据所申请的各专业和学校的要求参加。下面提供SAT2物理考试常用术语汇总的U-Z部分。

　　U

　　Uncertainty principle

　　A principle derived by Werner Heisenberg in 1927 that tells us that we can never know both the position and the momentum of a particle at any given time.

　　Uniform circular motion

　　The motion of a body in a circular path with constant speed.

　　Unit vector

　　A unit vector is a vector with length 1.

　　Universal gas constant

　　Represented by R = 8.31 J/mol · K, the universal gas constant fits into the ideal gas law so as to relate temperature to the average kinetic energy of gas molecules.

　　V

　　Vector

　　A vector quantity, or vector, is an object possessing, and fully described by, a magnitude and a direction. Graphically a vector is depicted as an arrow with its magnitude given by the length of the arrow and its direction given by where the arrow is pointing.

　　Velocity

　　A vector quantity dined as the rate of change of the displacement vector with time. It is to be contrasted with speed, which is a scalar quantity for which no direction is specified.

　　Vertex

　　The center of a mirror or lens.

　　Virtual image

　　An image created by a mirror or lens in such a way that light does not actually come from where the image appears to be.

　　W

　　Wave

　　A system with many parts in periodic, or repetitive, motion. The oscillations in one part cause vibrations in nearby parts.

　　Wave speed

　　The speed at which a wave crest or trough propagates. Note that this is not the speed at which the actual medium (like the stretched string or the air particles) moves.

　　Wavelength

　　The distance between successive wave crests, or troughs. Wavelength is measured in meters and is related to frequency and wave speed by = v/f.

　　Weak nuclear force

　　The force involved in beta decay that changes a proton to a neutron and releases an electron and a neutrino.

　　Weber

　　The unit of magnetic flux, equal to one T · m2.

　　Weight

　　The gravitational force exerted on a given mass.

　　Weightlessness

　　The experience of being in free fall. If you are in a satellite, elevator, or other free-falling object, then you have a weight of zero Newtons relative to that object.

　　Work

　　Done when energy is transferred by a force. The work done by a force F in displacing an object by s is W = F · s.

　　Work function

　　The amount of energy that metal must absorb bore it can release a photoelectron from the metal.

　　Work-energy theorem

　　States that the net work done on an object is equal to the object’s change in kinetic energy.

　　Z

　　Zeroth Law of Thermodynamics

　　If two systems, A and B, are in thermal equilibrium and if B and C are also in thermal equilibrium, then systems A and C are necessarily in thermal equilibrium.

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