AMPLITUDE:The term 'amplitude' refers to the physical
size of an oscillation.For sound waves in air,the amplitude
is the maximum distance an individual air molecule will move from its starting point as a sound wave passes by. The amplitude of a sound wave determines its loudness. A sound wave with a large amplitude will sound louder than a small amplitude wave.
BIG BANG:The big bang theory teaches that at a specific moment, the universe began as a very small, extremely dense mass that exploded outward in a violent explosion.According to the theory, the universe is continuing to expand today as a result of this initial explosion.The observed red shift of distant stars and galaxies is one of the primary pieces of evidence for the big bang theory.
BLUE SHIFT:The change in color toward the blue end of
the spectrum due to an object's motion toward the observer. The blue shift is a result of the frequency of light waves coming from an object being affected by the Doppler effect. It is only noticeable when objects are moving at very high speeds.
CONSTRUCTIVE INTERFERENCE:When two waves occupy the same space at the same time, their amplitudes add.If they add to produce a wave with a larger amplitude, they are said to be interfering constructively.
DESTRUCTIVE INTERFERENCE:When two waves occupy the same space at the same time,their amplitudes add.If they tend to cancel each other out in doing so,the waves are said to be interfering destructively.
DOPPLER EFFECT:The apparent change in frequency of a
sound wave. The Doppler effect can be caused by the motion of the source of the sound,the motion of the observer,or by the motion of both.
physicist and mathematician. J.C.Doppler first explained
the Doppler effect in 1842.
DOPPLER RADAR:Radar systems often utilize the Doppler
effect to measure velocity.A light wave emitted atan object will be reflected back at a different frequency if the object is moving.The change in frequency can then be used to determine the velocity.
EINSTEIN,ALBERT:(1879-1955).German-born American physicist.Einstein produced the theories of Relativity in the early 1900's that form the basis of modern physics. These theories gave scientists a different understanding of space and time, and also predicted the expansion of the universe.
FREQUENCY:The number of oscillations per unit time.
Frequency is commonly measured in oscillations per second, or Hertz.
GLOBAL POSITIONING SYSTEM:A network of satellites
which circle the globe and broadcast radio signals.These
signals are analyzed by GPS units on the ground to yield
information about position and speed.
HERTZ:The unit of measurement for frequency.One Hertz, or 1 Hz, is defined as one oscillation per second.
HUBBLE,EDWIN:(1889-1953).American astronomer.Hubble's observation of the Doppler effect in distant stars and galaxies help form the foundation of modern understanding of cosmology.Hubble observed that distant galaxies and stars are red shifted and therefore must be moving away from us at very high speeds.These observations are direct evidence that the universe expanding.
HUBBLE'S LAW:A mathematical principle that states that
the velocity at which a distant star or galaxy is receding
from Earth is directly proportional to its distance.The
relationship is expressed in the equation v = Hod where v
is the velocity of recession, Ho is the Hubble constant, and
is the distance of the receding object from Earth.The precise value of the Hubble constant is not known.
INFRASONIC:Below the frequency range of human hearing;below 20 Hz.Infrasonic sounds can be produced by thunder,earthquakes and heavy machinery.
INTERFERENCE:The superposition of two waves.When
two or more waves meet each other, the waves combine and form a new wave.The amplitude of this new wave at any point will be the mathematical sum of the amplitudes of the original waves.
LOUDNESS:How loud a sound is as heard by the ear.The loudness of a sound wave is determined by the amplitude
of the vibration.(Loudness is commonly referred to as
"volume",although this term is sometimes avoided in this context so that sound volume is not confused with spatial volume.)
MACH NUMBER:A number indicating speed as a multiple of the speed of sound.An object moving at Mach 1 would be moving at exactly the speed of sound.Mach 2 would be a speed twice that of sound,etc.
MACH,ERNST:(1838-1916).Austrian physicist and philosopher.
MEDIUM:The material through which a wave propagates.
For sound waves that we hear, the medium is commonly air. Light,or electromagnetic radiation,is the only example
of a wave that requires no medium through which to travel.
MODERN PHYSICS:Physics after the year 1900 is commonly known as modern physics.Based on Einstein's theories of relativity, and on the theories of quantum mechanics developed by Max Planck and Neils Bohr, modern physics replaces classical or Newtonian physics as a more current understanding of the world.
NEWTONIAN PHYSICS:Also known as "Classical Physics." Newtonian physics consists of the theories of
developed by Isaac Newton and those who came after him.
In the late 1800's, many scientists were confident that
Newtonian physics would provide the final and nearly
complete understanding of the world.After 1900, Newtonian physics was shown to be only a good approximation and was replaced by modern physics.
OCTAVE:A musical interval equivalent to doubling or
halving the frequency of a given note. A note that is one
octave higher will have twice the frequency; a note one
octave lower will have half the frequency.
PERIOD:The time for one complete oscillation;the time
for one complete wave front to pass; the time between
wave emissions.Period is the inverse of frequency and is
commonly measured in seconds.
PITCH:The quality of a sound or musical note generally
referred to as "high" or "low".A high pitched sound is
produced by a high frequency vibration.A low pitched
sound is produced by a low frequency vibration.On stringed instruments, high pitched sounds come from the shorter, smaller,and more tightly tuned strings.
RED SHIFT:The change in color toward the red end of the
spectrum due to an object's motion away from an observer.
The red shift is due to the Doppler effect. It is only noticeable when an object is moving extremely fast.
RELATIVITY:The common name for the theories put forth
by Albert Einstein in 1905 and 1915.The theory of relativity replaced Newtonian mechanics and revised common notions of space and time.The General Theory of Relativity predicted the expansion of the universe.
SHOCK WAVE:The large amplitude sound wave produced
by an object travelling at Mach one or faster.When an
object reaches the speed of sound,the sound waves it
produces can no longer outrun it.The sound waves "pile up" in the front of the object and interfere constructively to
produce one extremely large sound wave. At Mach 1, this
shock wave is in the front of the object.At speeds greater
than Mach 1,the shock wave takes on the shape of a cone
spreading out behind the object,similar to the wake behind
SONIC BOOM:The loud noise associated with a shock wave. Sonic booms are commonly caused by supersonic aircraft. From a distance,the sonic boom sounds similar to thunder. At close range it can be physically damaging or deafening. Because of the inherent possibilities of damage or injury from a sonic boom, aircraft generally do not travel at speeds of Mach 1 or greater at low altitudes over populated areas.
SOUND:The propagation of molecular vibrations through
a material. Sound is generally associated with waves
travelling through the air, but sound can travel through any
material. Any longitudinal wave passing through a material
can properly be referred to as a sound wave.
STEADY STATE THEORY: The theory that the universe
exists in a steady state, unchanging.According to the
steady state theory,the universe has always existed in its
present condition.Although it enjoyed wide acceptance at
one time,most scientists now believe that the universe has
not existed forever but had a beginning at a specific point
in time known as the big bang.
SUBSONIC:Slower than the speed of sound.Any speed
less than Mach 1 is referred to as subsonic.
SUPERSONIC:Faster than the speed of sound.Any speed
greater than Mach 1 is referred to as supersonic.
ULTRASONIC:Above the frequency range of human hearing;above 20,000 Hz.
VELOCITY:The speed at which something is moving in a
particular direction. Velocity is commonly measured in
meters per second. Velocity is a vector quantity and
always has a direction associated with it.
WAVE:A disturbance that propagates through a medium.
Waves can occur in any material.Light,or electromagnetic
radiation,can travel in a vacuum and is the only example of
a wave which requires no medium through which to travel.
WAVE FRONT:One individual wave pulse,sometimes
referred to as a single wave.When used in reference to
sound waves,the term generally refers to a single
compression region of the wave.
WAVELENGTH:The distance between two consecutive wave fronts.Wavelength is commonly measured in meters and is directly related to the wave's frequency and velocity according to the equation v = f .
YEAGER,CHUCK:American test pilot.Chuck Yeager was the first person to fly faster than sound in the experimental aircraft known as the X-1. 16
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