vendredi 24 août 2012
Correct wall size varies with native conditions
and climate; the number of insulation used; and
also the latitude of the vacant lot. the primary 2
parts have an effect on the speed of temperature
loss from an area, that is influenced by the number
lundi 20 août 2012
Sound is a vibration in an elastic medium such
as air, water, most building materials, and the earth.
(Noise can be defined as unwanted sound, that is,
annoying sound made by others or very loud sound
which may cause hearing loss.)
An elastic medium returns to its normal state after a
force is removed.
Pressure is a force per unit area. Sound energy progresses
rapidly,producing extremely small changes in atmospheric
pressure, and can travel great distances.
However, each vibrating particle moves only an infinitesimal
amount to either side of its normal position.
It “bumps’’ adjacent particles and imparts most of its motion
and energy to them.A full circuit by a displaced particle is called
a cycle. The time required for one complete cycle is called the
period and the number of complete cycles per second is
the frequency of vibration.
Consequently, the reciprocal of frequency is the period.
Frequency is measured in cycles per second, the unit for
which is called the hertz (abbreviated Hz).
A pure tone is vibration produced at a single frequency.
depicts the variation in pressure caused by striking a tuning
fork, which produces an almost pure tone by vibrating
adjacent air molecules.
Symphonic music consists of numerous tones at different
frequencies and pressures (that is, a tone is composed of a
fundamental frequency with multiples of the fundamental,
theprongs of the tuning fork alternately compress and
rarefy adjacent air particles. This cyclical motion causes a
chain reaction between adjacent air particles so that the
waves (but not the air particles) propagate away from the tuning fork.