ultrasonic- Term applied to sound frequencies above 20 000 hertz, the normal upper
limit of human hearing.
ultraviolet- Electromagnetic waves of frequencies
higher than those of violet light.
umbra- The darker part of a shadow where
all the light is blocked.
unstable equilibrium- The state of an object bal-anced
so that any small displacement or rotation lowers its center of gravity
universal
gravitational constant- The constant G in the equation for Newton's law of universal
gravitation; measures the strength of gravity
V- (a) The symbol for volt.
(b) In lowercase italic, the symbol for speed or velocity (c) In uppercase italic,
the symbol for voltage.
vector- An arrow whose length represents the magnitude
of a quantity and whose direction represents the direction of the quantity
vector
quantity- A quantity in physics, such as force, that has both magnitude and direction.
velocity- Speed together with the direction of motion.
vibration-
An oscillation, a repeating, back-and-forth motion, about an equilibrium position.
virtual image- An image formed through reflection or refraction that can
be seen by an observer but cannot be projected on a screen because light from the
object does not actually come to a focus.
watt- (WAT) The SI unit of power.
One watt is expended when one joule of work is done in one second.
wave-
A "wiggle in space and time"; a disturbance that repeats regularly in space
and time and that is transmitted progressively from one place in a medium to the
next with no actual transport of matter.
wave- front The crest, trough, or
any continuous por-tion of a two-dimensional or three-dimensional wave in which the
vibrations are all the same way at the same time.
wavelength- The distance
from the top of the crest of a wave to the top of the following crest, or equivalently,
the distance between successive identical parts of the wave.
weight- The
force on a body due to the gravitational attraction of another body (commonly the
earth).
weightlessness- The condition of free fall toward or around the earth,
in which an object experiences no support force (and exerts no force on a scale).
weight- density Weight of a substance divided by its volume.
white
light- Light, such as sunlight, that is a combination of all the colors. Under white
light, white objects appear white and colored objects appear in their individual
colors.
work- The product of the force on an object and the distance through
which the object is moved (when force is constant and motion is in a straight line
in the direction of the force); measured in joules.