1652 Chapter 48
S is the speed,
l is the length or distance,
t is the time to travel.
Speed is a scalar quantity as it is not referenced to
direction. Instantaneous speed =dl»dt. Velocity is the
rate of increase of distance traversed by a body in a
particular direction.
Velocity is a vector quantity as both speed and direc-
tion are indicated. The l »t can often be the same for the
velocity and speed of an object, however, when speed is
given, the direction of movement is not known. If a
body describes a circular path and each successive equal
distances along the path is described in equal times, the
speed would be constant but the velocity would
constantly change due to the change in direction.
Weight. Weight is the force exerted on a mass by the
gravitational pull of the planet, star, moon, etc., that the
mass is near. The weight experienced on earth is due to
the earth’s gravitational pull, which is 9.806 65 m/s^2 ,
and causes an object to accelerate toward earth at a rate
of 9.806 65 m/s^2 or 32 ft/s^2.
The weight of a mass M is M(g). If M is in kg and g
in m/s^2 , the weight would be in newtons (N). Weight in
the U.S. system is in pounds (lb).
Acceleration. Acceleration is the rate of change in
velocity or the rate of increase or decrease in velocity
with time. Acceleration is expressed in meters per
second squared (m/s^2 ), or ft/s^2 in the U.S. system.
Amplitude. Amplitude is the magnitude of variation in
a changing quantity from its zero value. Amplitude
should always be modified with adjectives such as peak,
rms, maximum, instantaneous, etc.
Wavelength (M). In a periodic wave, the distance
between two points of the corresponding phase of two
consecutive cycles is the wavelength. Wavelength is
related to the velocity of propagation (c) and frequency
(f) by the equation
(48-21)The wavelength of a wave traveling in air at sea
level and standard temperature and pressure (STP) is
(48-22)or
(48-23)For instance, the length of a 1000 Hz wave would be
0.33 m, or 1.09 ft.Phase. Phase is the fraction of the whole period that has
elapsed, measured from a fixed datum. A sinusoidal
quantity may be expressed as a rotating vector OA.
When rotated a full 360 degrees, it represents a sine
wave. At any position around the circle, OX is equal in
length but said to be X degrees out of phase with OA.
It may also be stated that the phase difference
between OA and OX is D. When particles in periodic
motion due to the passage of a wave are moving in the
same direction with the same relative displacement,
they are said to be in phase. Particles in a wave front are
in the same phase of vibration when the distance
between consecutive wave fronts is equal to the wave-
length. The phase difference of two particles at
distances X 1 and X 2 is(48-24)Periodic waves, having the same frequency and
waveform, are said to be in phase if they reach corre-
sponding amplitudes simultaneously.Phase Angle. The angle between two vectors repre-
senting two periodic functions that have the same
frequency is the phase angle. Phase angle can also be
considered the difference, in degrees, between corre-
sponding stages of the progress of two cycle operations.Phase Difference (I). Phase difference is the differ-
ence in electrical degrees or time, between two waves
having the same frequency and referenced to the same
point in time.Phase Shift. Any change that occurs in the phase of one
quantity or in the phase difference between two or more
quantities is the phase shift.Phase Velocity. The phase velocity is when a point of
constant phase is propagated in a progressive sinusoidal
wave.Temperature. Te m p e r a t u re is the measure of the
amount of coldness or hotness. While kelvin is the SI
standard, temperature is commonly referenced to °C
(degrees Celsius) or °F (degrees Fahrenheit).O c
f=--O 331.4 m/s
f=------------------------O 1087.42 ft/s
f=-----------------------------D2 S X 2 – X 1
O= ------------------------------