“Sound Waves”
Sound Waves Carry Energy
Sound energy ​
can be carried away from its source by a wave​
. The interesting
thing is that the material through which sound travels does not move with the
energy. ​
Sound waves often travel through air, but the air does not move with
the sound. If air did travel with sound, you would feel a rush of air every time
you heard the phone ring!
Sound Energy Travels through a Medium
Sound waves require a medium. A ​
medium​
is a substance through which sound
can travel.​
A medium can be any ​
one of the three states of matter: solid,
liquid, or gas. ​
When a particle (medium) vibrates, it ​
can pass its energy to a
particle next to it​
. As a result the second particle will move back and forth in
a way just like the first particle and so on.​
Most of the sounds you hear travel
through the air at least for part of the time.​
But sound waves can also travel
through other substances such as water, glass and metal.
What would happen if a tree fell in a vacuum (completely empty space, with all
air taken out)? No sound would be created because in a vacuum, there are no
air particles to vibrate. ​
If there is no medium (ex. air) there is no sound!
Sound cannot travel in a vacuum. No air-No sound!! ​
Sound must travel through
a medium for our ears to detect or hear it.
Longitudinal Sound Waves
Sound waves can be grouped together based on the direction that particles of
the medium vibrate compared to the direction in which the waves travels.
Sound travels in longitudinal waves. ​
In a ​
longitudinal wave​
,​
the particles of
the medium vibrate back and forth along the path that the wave travels.
Longitudinal waves are ​
made up of compressions and rarefactions.
A​
slinky​
can be compared to a longitudinal sound wave. When you push the end
of the slinky together, the coils of metal are crowded together. When a
section of​
particles are crowded together, it is called ​
compression​
. When you
pull back on the slinky, the coils are less crowded and more stretched out. A
section where p​
articles are less crowded is called r​
arefaction​
. Since sound
waves are examples of longitudinal waves, sound waves travel by compressions
and rarefactions.
​Pushing a slinky back and forth
creates a longitudinal wave.
The coils of the slinky move back
and forth, but do not travel with the wave.
Properties of Waves
Sound waves have certain properties. One property of a sound wave is the
height of the wave​
. This is known as ​
amplitude​
. The amplitude of a wave is the
maximum distance the wave vibrates from its rest position. The rest position
is where the particles of a medium stay when there are no disturbances. The
larger the amplitude, the taller the wave…and the more energy the wave
possesses and the louder the sound is!​​
Another property of sound is
wavelength​
.A​
wavelength is the distance between any two compressions or
any two rarefactions in a series of waves.​
Wavelengths are ​
measured from
one highest point to the next highest point​
on a sound wave. This is called
measuring from “​
crest to crest​
”.