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U–Z
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 defined 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 before 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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