Sound is a vibration that travels in waves through a medium like air or water. It is caused by vibrating objects and radiates outward in all directions. When these vibrations reach the ear, they are interpreted by the brain as sound. Sound waves are longitudinal waves that cause alternating compressions and rarefactions in the medium as they propagate. For sound to travel, it requires a material medium like air, water or other solids and liquids. As sound waves travel, they can be reflected, refracted or attenuated by the medium. The human ear collects sound pressure waves which are amplified through the middle and inner ear where fluid-filled chambers containing hair cells detect vibrations and transmit nerve signals to the brain.

1. PHYSICS PRESENTATION ON
SOUND
Submitted to-Mrs. Balpreet
Kaur
Submitted by-Swati
Class-IX B
Roll no.-3

2. What is
sound?All sounds are vibrations traveling
through the air as sound waves. Sound
waves are caused by the vibrations of
objects and radiate outward from
their source in all directions. A
vibrating object compresses the
surrounding air molecules (squeezing
them closer together) and
then rarefies them (pulling them
farther apart). Although the
fluctuations in air pressure travel
outward from the object, the air
molecules themselves stay in the same
average position. As sound travels, it
reflects off objects in its path,
creating further disturbances in the
surrounding air. When these changes
in air pressure vibrate your eardrum,
nerve signals are sent to your brain
and are interpreted as sound.

3. Propagation of sound
Sound is a sequence of waves of pressure that propagates
through compressible media such as air or water. (Sound can
propagate through solids as well, but there are additional
modes of propagation). Sound that is perceptible by humans
has frequencies from about 20 Hz to 20,000 Hz. In air
at standard temperature and pressure, the corresponding
wavelengths of sound waves range from 17 m to 17 mm. During
propagation, waves can be reflected, refracted,
or attenuated by the medium.

4. Sound needs a medium to travel!
Electric bell is suspended inside an
airtight glass bell jar An electric bell is
suspended inside an airtight glass bell
jar connected to a vacuum pump. As the
electric bell circuit is completed, the
sound is heard. Now if the air is slowly
removed from the bell jar by using a
vacuum pump, the intensity of sound
goes on decreasing and finally no sound
is heard when all the air is drawn out.
We would be seeing the hammer
striking the gong repeatedly. This
clearly proves that sound requires a
material for its propagation.
Sound can propagate not only through
gases but also through solids and
liquids. Some materials like air, water,

5. Sound waves are longitudinal waves
Sound is transmitted through
gases, plasma, and liquids
as longitudinal waves, also
called compression waves.
Through solids, however, it can
be transmitted as both
longitudinal waves and transverse
waves. Longitudinal sound waves
are waves of
alternating pressure deviations
from the equilibrium pressure,
causing local regions
of compression and rarefaction,
while transverse waves (in solids)
are waves of alternating shear
stress at right angle to the
direction of propagation.
Matter in the medium is
periodically displaced by a sound
wave, and thus oscillates. The
energy carried by the sound wave
converts back and forth between
the potential energy of the
extra compression (in case of

6. Characteristics
of sound Wavelength-In physics,
the wavelength of a sinusoidal wave is
the spatial period of the wave—the
distance over which the wave's shape
repeats. It is usually determined by
considering the distance between
consecutive corresponding points of
the same phase, such as crests,
troughs, or zero crossings, and is a
characteristic of both traveling waves
and standing waves, as well as other
spatial wave patterns.
Amplitude-The amplitude of
a periodic variable is a measure of its
change over a single period (such
as time or spatial period). There are
various definitions of amplitude, which
are all functions of the magnitude of
the difference between the
variable's extreme values.

7. Frequency -Frequency is the number of
occurrences of a repeating event per
unit time. It is also referred to
as temporal frequency, which
emphasizes the contrast to spatial
frequency and angular frequency.
Intensity-Sound intensity or acoustic
intensity (I) is defined as the sound
power Pac per unit area A.The usual
context is the noise measurement of
sound intensity in the air at a listener's
location as a sound energy quantity.
Speed of sound-The speed of sound is
the distance travelled during a unit of
time by a sound wave propagating
through an elastic medium. In dry
air at 20 °C (68 °F), the speed of sound
is 343.2 meters per second (1,126 ft/s).
This is 1,236 kilometers per hour
(768 mph).
ˆ

8. Reflectionofsound
The reflection of sound follows the law "angle of incidence equals
angle of reflection", sometimes called the law of reflection. The
same behavior is observed with light and other waves, and by
the bounce of a billiard ball off the bank of a table. The
reflected waves can interfere with incident waves, producing
patterns of constructive and destructive interference. This can
lead to resonances called standing waves in rooms. It also
means that the sound intensity near a hard surface is
enhanced because the reflected wave adds to the incident
wave, giving a pressure amplitude that is twice as great in a
thin "pressure zone" near the surface. This is used in pressure
zone microphones to increase sensitivity. The doubling of
pressure gives a 6 decibel increase in the signal picked up by
the microphone. Reflection of waves in strings and air
columns are essential to the production of resonant standing
waves in those systems.

9. Humanear The outer part of the ear collects sound. That sound pressure is amplified through the middle
portion of the ear and, in land animals, passed from the medium of air into a liquid medium. The
change from air to liquid occurs because air surrounds the head and is contained in the ear canal
and middle ear, but not in the inner ear. The inner ear is hollow, embedded in the temporal bone,
the densest bone of the body. The hollow channels of the inner ear are filled with liquid, and
contain a sensory epithelium that is studded with hair cells.
