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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