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2. Speed of Sound and Density
Sound waves can travel through other materials besides air. The speed
in which sound travels in a given highly depends on the density of the
medium. In fact, sound is usually fastest in solids where its atoms or
molecules are closest together, and slowest in gases where molecules are
farthest apart.

3. Speed and Elasticity
The elasticity of a material also affects the speed of sound. The elastic
property of a material refers to its tendency to maintain its shape and not
deform when a force is applied to it. Rigid materials such as steel will
experience a smaller deformation than rubber when a force is applied to it
because rubber is more flexible.
Elastic materials vibrate at lower speeds because their particles return to
their original positions at lower rates. Thus, sound travels very slowly in elastic
materials than rigid materials. In fact, these types of materials, such as rubber,
can be used for soundproofing.

4. Speed and Temperature
Sound travels faster if it is hotter. As a substance heats up, its molecules
move faster, so they collide more frequently. The more frequent the collisions are
the faster the speed of sound is in material.
The speed of sound in an ideal gas v, for example, in a given temperature
T in Kelvin is given by:
v = vo
(Equation 1)
where vo is the speed of sound at absolute temperature To.
𝑇
𝑇𝑜

5. For air, the speed of sound in air can be approximated using the
equation:
v = 331 m/s + (0.606
𝑚/𝑠
°
) Tc (Equation 2)

6. where Tc is the temperature of the air in °C. For every 1
°C rise intemperature, the speed of the air increases by 0.606
m/s.
Other factors such as humidity and pressure, can also
affect the
speed of sound in air.

7. R
RE
EF
FL
LE
EC
CT
TI
IO
ON
N O
OF
F S
SO
OU
UN
ND
D
• The reflection of sound follows the same
lawsas for reflection of light
– angle of incidence = angle of reflection
– the incident wave, the reflected wave and
thenormal lay in the same plane.
• Sound waves can be reflected by large,

8. hard,smooth, vertical and faraway
surfaces, e.g. walls, buildings and cliffs.
• Echoes are produced by the
reflections ofsounds from such
surfaces.
1

9. R
RE
EV
VE
ER
RB
BE
ER
RA
AT
TI
IO
ON
N
• This occurs when the original and reflected sounds
are so close that the two cannot be heard as separate
sounds. The original soundjust seems prolonged.
Applications of Echo
1 To find submarines from surfaceships.

10. 2 In fishing boats, to find large shoalsof fish.
3 To measure the depth of the sea.
4 to locate a sunken shipwreck orcargo

11. Thank You!