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- walk-around bottle
- A personal supply of oxygen for the use of crewmembers when temporarily
disconnected from the craft's system.
- walled plain
- See lunar
- Short for apparent
- waning moon
- The moon between full and new when its visible part is decreasing. See phases
of the moon.
- Originally the part of a missile carrying the explosive, chemical, or
other charge intended to damage the enemy. By extension, the term is sometimes
used as synonymous with payload or nose cone .
- warmup time
- The time interval required for a gyro to reach
specified performance from the instant that it is energized.
- Dihydrogen oxide (molecular formula H20). The word is used ambiguously to
refer to the chemical compound in general and to its liquid phase; when the
former is meant, the term water substance is often used.
- Water is distinguished from other common terrestrial substances in
existing in all three phases at atmospheric temperatures and pressures (see ice, water
vapor). The phase changes, are of great significance in many geophysical
processes. The same is true of the large specific heat of liquid water and ice
relative to both land surface and atmosphere. Water's complex absorption
spectrum gives rise to the greenhouse
- waterfall effect = Lenard effect.
- water-flow pyrheliometer
- An absolute pyrheliometer,
developed by C. G. Abbot, in which the radiation-sensing element is a
blackened water calorimeter.
- It consists of a cylinder blackened on the interior and surrounded by a
special chamber through which water flows at a constant rate. The temperatures
of the incoming and outgoing water, which are monitored continuously by
thermometers, are used to compute the intensity of the radiation. This
instrument is used by the Smithsonian Institution as its standard instrument.
- water substance
- See water.
- water suit
- A g-suit
in which the fluid used in the interlining is a liquid, thereby automatically
approximating the required hydrostatic pressure gradient under acceleration.
- water vapor
- Water (H2O) in gaseous form. Also called aqueous vapor . See vapor.
- The amount of water vapor present in a given gas sample may be
expressed in a number of ways. See absolute
ratio, dewpoint, relative
- water-vapor absorption
- The absorption of certain wavelengths of infrared
radiation by atmospheric water
vapor. See absorption
- The water-vapor absorption spectrum is composed of bands near 1.4, 1.8,
2.7, and 6.3 microns and a series of bands beginning at 11 microns and growing
stronger with increasing wavelength.
- watt (abbr w, W)
- The unit of power in the MKSA system; that
power which produces energy at the rate of 1 joule per second.
- A disturbance which is propagated in a medium in such a manner that at any
point in the medium the quantity
serving as measure of disturbance is a function of the time, while at any
instant the displacement
at a point is a function of the position of the point.
- Any physical quantity that has the same relationship to some
independent variable (usually time) that a propagated disturbance has, at a
particular instant, with respect to space, may be called a wave.
- wave equation
- The partial differential equation of the form
where is usually a function of the position and time
coordinates; 2 is the Laplacian operator; t is the time;
and C2 is a constant. Also called equation of wave
motion . See wave, gravity
- The general solution to this equation is any function defined over a
plane, the phase front, moving perpendicular to itself at the speed c.
- wave filter
- A transducer
for separating waves on the
basis of their frequency. It
introduces relatively small loss to waves in one or more frequency bands and
relatively large loss to waves of other frequencies. Also called filter
- The graphical representation of a wave, showing
variation of amplitude
- wave front = phase front.
- A system of boundaries capable of guiding wave.
- wave interference
- The phenomenon which results when waves of the same or nearly the same frequency are
superposed; characterized by a spatial or temporal distribution of amplitude of
some specified characteristic differing from that of the individual superposed
waves. Also called interference .
- In general, the mean distance between maximums (or minimums) of a roughly
pattern. Specifically, the least distance between particles moving in the same
phase of oscillation
in a wave
- The wavelength is measured along the direction of propagation of the
wave, usually from the midpoint of a crest (or trough) to the midpoint of the
next adjoining crest (or trough). It is related to frequency f and phase speed
v by λ = v / f , where λ is wavelength. The reciprocal of wavelength is
- See Huygens
- wave motion
- The oscillatory motion of the particles of a medium caused by the passage
of a wave,
produced by forces external to the medium, but propagated through the medium
by internal forces. Wave motion per se involves no net translation of the
- Various types of oscillation
are found in natural wave motions. Among the simplest are the linear
oscillation parallel to the direction of propagation of a longitudinal wave,
the linear oscillation perpendicular to the direction of propagation of a
transverse wave, and the orbital motion produced by the passage of a
progressive gravity wave.
- wave number (symbol )
- The reciprocal of wavelength;
the number of waves per unit distance in the direction of propagation;
or, sometimes 2π times this quantity.
- In spectroscopy, wave number is usually expressed in reciprocal
centimeters, as 100,000 cm-1 (100,000 per centimeter).
- wave of translation
- A wave in
which the individual particles of the medium are shifted in the direction of
wave travel, as ocean waves in shoal waters; in contrast with an oscillatory
wave, in which only the form advances, the individual particles moving in
closed orbits, as ocean waves in deep water.
- wave speed = phase velocity.
- wave theory of light
- See electromagnetic
- wave train
- A limited series of waves caused by a
periodic disturbance of short duration, e.g., the radiofrequency waves in a
single pulse, or a succession of pulses themselves.
- wave velocity = phase
- The wall of a grain or propellant with an internal cavity.
- weber (abbr wb)
- The unit of magnetic
flux; the magnetic flux which, linking a circuit of one turn, produces in
it an electromotive force of 1 volt as it is
reduced to zero at a uniform rate in 1 second.
- Weber-Fechner law
- An approximate psychophysical law relating the degree of response or
sensation of a sense organ and the intensity of the stimulus. The
law asserts that equal increments of sensation are associated with equal
increments of the logarithm of the stimulus, or that the just noticeable
difference in any sensation results from a change in the stimulus which bears
a constant ratio to the value of the stimulus. Also called Weber law .
- The Weber-Fechner law is applied to the detection of contrast in the
problem of visual range, as well as to many other psychophysical problems.
- Weber law = Weber-Fechner law.
- weight (symbol w )
- 1. The force with which
a body is attracted toward the earth.
- 2. The product of the mass of a body and
acting on a body.
- In a dynamic situation, the weight can be a multiple of that under
resting conditions. Weight also varies on other planets in accordance with
- weight flow rate (symbol )
- Mass flow rate multiplied by gravity, or
= ( dm/dt ) g = mg Where m
is mass and t is time; usually expressed in pounds per second.
- 1. A condition in which no acceleration, whether of gravity or
other force, can be detected by an observer within the system in
- Any object failing freely in a vacuum is weightless, thus an
unaccelerated satellite orbiting the earth is weightless although gravity
affects its orbit. Weightlessness can be produced within the atmosphere in
aircraft flying a parabolic flightpath.
- 2. A condition in which gravitational and other external forces acting on
a body produce no stress, either internal or external, in the body.
- Joining two or more pieces of metal by applying heat, pressure, or both,
with or without filler material to produce a localized union through fusion or
recrystallization across the interface.
- The thickness of the filler material is much greater than the capillary
dimensions encountered in brazing.
- To come in contact with, and flow across (a surface, body, or area) - said
of air or other fluid.
- wet emplacement
- A launch
emplacement that provides a deluge of water for cooling the flame
bucket, the rocket
engines, and other equipment during the launch of a missile. See flame
- wet-fuel rocket = liquid rocket.
- A radiofrequency
electromagnetic signal generated
by some lightning discharges.
- This signal apparently propagates along a geomagnetic line of force and
often bounces several times between the Northern and Southern Hemispheres. Its
name derives from the sound heard on radio receivers.
- whistling meteor
- Name applied to a radio
meteor when a detection system is used in which the presence of the meteor
is indicated by a rapidly changing audiofrequency
- The maximum reflection of a radio signal from a radio meteor occurs
when the ion column is perpendicular to the line from the column to the
transmitter-receiver. During the approach of the meteor to this position, the
Doppler effect causes a change in the frequency of the reflected signal. When
the reflected signal frequency is then combined with the transmitter
frequency, the difference between the transmitted and reflected frequencies
produces an audiofrequency beat. The audiofrequency beat, when amplified and
fed to a loudspeaker, allows the meteors to be heard as a high-pitched whistle
which rapidly falls to zero frequency as the meteor trail becomes normal to
the line of sight.
- white body
- A hypothetical body whose surface absorbs no electromagnetic
radiation of any wavelength, i.e., one which exhibits zero absorptivity
for all wavelengths; an idealization exactly opposite to that of the black
body. See gray
- In nature, no true white bodies are known. Most white pigments
possessing high reflectivity for visible radiation are fairly good absorbers
in the infrared; hence, they are not white bodies in the sense of the
radiation theory. However, the term white body is used for physical objects
with respect to a particular wavelength interval.
- white noise
- A sound or
wave whose spectrum is continuous and uniform as a function of frequency.
- white room
- A clean and dust-free room used for assembly and repair of precise
mechanisms such as gyros.
- Wien displacement constant
- See Wien
- Wien displacement law = Wien law.
- Wien distribution law
- A relation, derived on purely thermodynamic
reasoning by Wien, between the monochromatic emittance of
an ideal black body
and that body's temperature, Jλ/T5 = f(λ, T) where
Jλ is the monochromatic emittance
(emissive power) of a black body at wavelength λ and absolute temperature T, and f(λ, T) is a function which cannot be determined
purely on classical thermodynamic grounds. Compare Wien law.
- Wien law
- One of the radiation
laws which states that the wavelength of maximum radiation intensity for
body is inversely proportional to the absolute
temperature of the radiating black body: λm = b/T where λm is the wavelength of maximum intensity; b
is a constant; and T is the absolute temperature. The Wien
displacement constant b is equal to 0.28978 centimeter-degree. Also called
Wien displacement law .
- This law, established experimentally by Wien in 1896, describes the
manner in which the wavelength of maximum radiation shifts toward shorter
values as the temperature of a radiator rises. It is to be distinguished from
distribution law which describes the variation with temperature of the
intensity of emission at any wavelength. Wien displacement law is used to
compute the color temperature of a radiator by insertion of its wavelength of
peak intensity into the above equation to compute T.
- wind axis
- Any one of a system of mutually perpendicular reference axis established
with respect to the undisturbed wind direction about an aircraft or similar
body. See axis,
- 1. Any device introduced into the atmosphere for producing an appreciable
usually for tracking some airborne device or as a tracer of wind.
- 2. A World War II code name for a type of radar-jamming
device employed to confuse the operators of enemy radars (also referred to by
the code names of rope, chaff , and clutter ).
- One type of window consists of packages containing thousands of small
strips of paperbacked tinfoil which may be dropped from aircraft and balloons,
ejected from rockets, and carried within balloons. The packages burst open
upon ejection, scattering the tinfoil widely, producing a radar echo which
looks like a small shower or a tight formation of aircraft on
- 3. Any gap in a linear continuum, as
atmospheric windows , ranges of wavelengths in the
electromagnetic spectrum to which the atmosphere is transparent, or firing
windows , intervals of time during which conditions are favorable for
launching a spacecraft on a specific mission.
- wind shear
- See barotropic
- wind tunnel
- A tubelike structure or passage, sometimes continuous, together with its
adjuncts, in which a high-speed movement of air or other gas is produced, as
by a fan, and within which objects such as engines or aircraft, airfoils,
rockets (or models of these objects), etc., are placed to investigate the airflow about
them and the aerodynamic
forces acting upon them.
- Tunnels are designated by the means used to produce the gas flow, as
hot shot tunnel, arc tunnel, blow down tunnel; by the speed range, as
supersonic tunnel, hypersonic tunnel; or by the medium used, as plasma tunnel,
light gas tunnel.
- wind-tunnel balance
- A device or apparatus that measures the aerodynamic forces and moments acting
upon a body tested in a wind
- winter solstice
- 1. That point on the ecliptic
occupied by the sum at maximum southerly declination.
Sometimes called December solstice, first point of Capricornus .
- 2. That instant at which the sun reaches the point of maximum southerly
declination, about December 22.
- Sometimes used as the equivalent of radio, particularly in British
- wire link telemetry
- Telemetry in
which no radio
link is used. Also called hard wire telemetry .
- Wolf number = relative sunspot number.
- Wolf-Wolfer-Wolfest number = relative sunspot number.
- In electronic computers, an ordered set of characters
which is the normal unit in which information
may be stored, transmitted, or operated upon within a computer.
- word rate
- In computer
operations, the frequency
derived from the elapsed period between the beginning of transmission of one
word and the
beginning of transmission of the next word.
- work (symbol W )
resulting from the motion of a system against a force and
existing only during the process of energy conversion.
- work function
- The energy required
for an electron to
escape a solid surface. See Helmholtz
- In ion engines, the work function of the ionizer must be greater than
potential of the neutral atoms in the propellant gas.
- working fluid
- A fluid
(gas or liquid) used as the medium for the transfer of energy from one
part of a system to
- World Geographic Reference System
- A geographic reference system for the world, used in the Air Force for
aircraft position reports and target designation, and for the control and
direction of air units engaged in air defense, air-sea rescue, and tactical
- The short title for this system is georef.
- In computer terminology, record.