MECHANICAL WAVES

1. Sound

2. OSound is a form of energy that is
transmitted through matter as
waves called sound waves.
OMechanical waves, such as
sound waves, water waves, and
waves traveling on a spring, are
waves that require a medium
(solid, liquid, or gas) to travel.

3. TYPES OF MECHANICAL WAVES
1. Transverse waves are waves that
travel perpendicular to the direction
of the vibrations of the particles of the
medium.
- It occurs only in a solid material.
- When rope that is fixed horizontally is
disturbed in the vertical direction, a
transverse wave that moves
horizontally is created while the
particles of the rope move vertically.

4. The trough is the lowest part of a transverse wave
while the crest is the highest
The compressions resemble the trough while the
rarefactions are the crests.

5. 2. Longitudinal waves are waves that
travel parallel to the direction of the
vibrations of the particles of the
medium.
A longitudinal waves passes through
any medium (solid, liquid, gas)
When a slinky coil is pushed and pulled
at one end, a longitudinal wave is
created.

8. Oin a transverse wave, the
movement of particles is
perpendicular to the direction of
wave travel. In a longitudinal
wave, on the other hand, travel
is parallel to the movement of
the particles

9. OThe distance from one compression to
the next or between two successive
compressions in a longitudinal wave
equals the wavelength. If you count the
number of compressions passing by a
certain point in 1 second, you are able to
determine the frequency of the
longitudinal wave. If you multiply the
measured wavelength and the computed
frequency you will be able to determine
the speed of the wave. In equation,

10. Speed of Sound
OThe speed of sound in any medium is
dependent on the temperature,
elasticity, and density of the medium.
OTemperature effects the motion of the
particles of a medium.
OThe higher the temperature of the
medium, the faster the particles of the
medium move:, thus the faster the
sound travels in the medium.

11. OIt follows that the sound travels faster
in the air when day is warm than when
a day is cold.
OElasticity allows transfer of energy
from one particle to another particle of
a medium.
OIn an elastic medium, when its particle
are disturbed, they return to their
original positions easily; allowing faster
transmission of sound.

12. OSolids are generally more
elastic than liquids, while
liquids are more elastic than
gas.
OFor a given volume, the mass
of a denser material is greater
than that of the less dense

13. OHence particles in the denser
material have more inertia than
those in the less dense material.
It follows that the particles of the
less dense material can be
moved more quickly that those
of the denser materials.

14. OGenerally, sound travels faster in
solids than in gases due to the
molecular arrangement of solid
material.

15. At higher temperatures, particles have
more energy (kinetic) and thus, vibrate
faster. And when particles vibrate faster,
there will be more collisions per unit
time. With more collisions per unit time,
energy is transferred more efficiently
resulting in sound traveling quickly.
Sound travels at about 331 m/s in dry
air at 0°C.

16. The speed of sound is dependent on
temperature of the medium where an increase
is observed with an increase in temperature.
O This means that at temperatures greater than
0°C speed of sound is greater than 331 m/s by
an amount 0.6
𝑚/𝑠
𝐶
of the temperature of the
medium. In equation,

18. Properties of Sound
Ultrasound image Live concert
Ultrasound works on the principle of reflection of sound waves
while concerts in open field benefit from refraction of sound.

19. OReflection is usually described as the
turning back of a wave as it hits a barrier.
Echo is an example of a reflected sound.
Reverberation on the other hand refers to
the multiple reflections or echoes in a
certain place. A reverberation often occurs
in a small room with height, width, and
length dimensions of approximately 17
meters or less.
OThis best fits the bathroom which enhances
the voice.

20. Reflection of Sound
Bathroom singing
A study conducted noted that
people would open their mouths
wide when they sing in private
places like the baths. Another
reason is the hard wall surfaces of
the bathroom usually made of wood
or tiles brings about multiple
reflection of sound. These hard
walls or surfaces and the small
dimension of the bathroom typically
create an aurally pleasing acoustic
environment with many echoes and
reverberations contributing to
the fullness and depth of voice.

21. SONAR
Echo sounding is another application of sound
reflection. This is used by scientists to map the sea
floor and to determine the depth of the ocean or
sea. This is just the same as how bats use sound
to detect distances.

22. Refraction of Sound
Sound refraction at day time Sound refraction at night time

23. Sound is heard better in far areas during
nighttime than during daytime. This happens
due to what is known as refraction. Refraction
is described as the change in speed of sound
when it encounters a medium of different
density.
Sound travels faster in hotter media.
This change in speed of sound during
refraction is also manifested as sort of
“bending” of sound waves.

24. OWhen sound propagates in air, where the
temperature changes with altitude, sound
bends towards the hotter region. In this
case, refraction happens. The refraction
is due to the different refractive indices of
air because of the difference in
temperature. At daytime, when the sun is
shining, the air near Earth’s surface is
cooler than the air above.

25. O At night time, the air near the Earth’s surface
is heated by the heat emitted by the ground,
making it hotter than the air above which is
cooler due to the absence of the sun during
nighttime. This makes sound move from the
cooler air above towards the hotter air near the
earth’s surface.
O This makes open field concerts better done
during nighttime as sound waves are refracted
from the stage towards the audience. This
gives a clearer and more audible music to
enjoy.