Leon Papadopoulos
Prof. Hecht
Physics 113
Due:
Research
Paper: Waves and Sounds
Whether people realize it or not, waves and
sounds are transferred constantly throughout the course of the day. They play a huge role in the mechanics of
physics. Waves and sounds go hand-in-hand with each
other because sound is a certain type of waves. Sound is a particular kind of wave known as
a compression wave.
Sound can be defined in many different ways. To non-physicists sound is simply just what
people can hear. The
actual definition of sound is a “compression wave with its frequency in the
range of 20 Hz and 20 kHz” (Hecht 448). It can also be defined as a vibration of or within any
substance. Vibrations move
through each molecule of the substance causing sound waves to emerge throughout
the object. As the wave
goes through the substance each of the molecules within the substance strike
each other, and then bounce back into their original position. Sound can travel practically through any
substance. The only places
it can not go through are vacuums. A vacuum is an area with out matter.
As mentioned before sound is a type of
compression wave. A
compression wave can be defined as a wave that condenses the medium in which it
passes through. Compression
waves can also be referred to as mechanical longitudinal waves or pressure
waves. As compressive waves pass through solid
substances they are known as longitudinal elastic waves. When a wave passes through liquids it is
referred to as an acoustic wave.
“The propagation of a compression wave takes place in the direction along which
the particles of the medium oscillate, and it is marked by a series of
alternate condensations and rarefactions.” (Hecht 458).
Condensation is where the density of an elastic medium changes constantly from
its average value as a compression wave goes through it. Rarefaction is a reduction in of density as
a sound wave passes through the medium of an object.
The three main parts of a wave are its amplitude,
frequency, and phase. The
amplitude of a wave can be calculated by subtracting the wave’s highest point
by its lowest point, then dividing them by two. The amplitude informs us of the highest
displacement during one oscillation. The dictionary definition of phase is “a
particular stage or point of advancement in a cycle; the fractional part of the
period through which the time has advanced, measured from some arbitrary origin
often expressed as an angle (phase angle), the
entire period being taken as 360°.” (“Phase” www.Dictionary.com)
The Frequency of a wave is how many cycles the wave completes in a certain
period of time. The period of the wave is the time elapsed for a cycle.
If a wave has a
high frequency its period is shorter then that of a low frequency wave. Also
the higher the frequency in a sound wave, the louder the pitch will be.
The speed of sound varies in solids, liquids,
and gases. Each of these
has a certain effect on sound waves as they pass through them. Sound waves travel fastest through solids
out of the three mediums, and travels through gas the slowest. This is true for many reasons. Sound waves pass quickest through solids
because molecules in solid object are much closer together then in liquids and
especially gasses. Everything
is compacted tightly together in solids. Even though the speed of sound is higher in the majority of
solids, this is not true for all of them. Some objects have a higher speed in liquids then in solids. Many animals use sound waves in oceans or
rivers to communicate.
This is a very efficient way for them to communicate because the sound waves
travel so fast and cover huge distances. Sound travels the slowest through gasses by far because the
molecules are so far spread apart. Sound waves bounce off the molecules within the median, as
explained prior to this. Listed
below is a table of how fast sound travels through certain objects.
f(Thinkquest.org)
According
to the table sound travels fasted through steel objects and slowest through the
gas carbon dioxide.
Another
huge part of sounds and waves is the Doppler Effect. The Doppler Effect can basically be defined as the change
of the level and tone of a sound wave because of the rate the object is moving
at with respect to the person hearing it. This
is a fascinating part of physics because the depending on where a person is
with respect to the object making noise, the sound will be higher pitched or lower
pitched. For example, if a police officer is
speeding towards you with his sirens on, his sirens would be very high pitched. If you compare this to a police officer going in the
opposite direction of you the sound tone would be much lower. This is so because the waves in front of the police car are
being compressed together as they come towards you. Since there is more compressions of the waves when the car
is going towards you there is more vibrations that would reach your ears at a
high frequency. If the
police car was traveling further away there would be a lot less vibrations per
second which would cause the sound not to be as loud.
The
Doppler Effect can only be observed when the object moving is traveling with a
lower rate then a sound wave travels. The
object must be traveling slower then 330 meters per second which is the speed
of sound. If the object surpasses this speed a
sonic boom can be heard. A
sonic boom is a very high toned sound that is caused by shockwaves as they
break the speed of sound.
Diffraction
also plays a big role in sound waves and how they travel and move around
things. An example of diffraction is when there is an object in front of a
sound wave it would bend around it. The sound wave will not physically go
through it, but it will find its way around. If sound waves did not use
diffraction they would only be contained in areas without objects blocking the
sound wave path. This is true because if someone is listening to music in one
room it could be heard from the next room even if the door is closed. To
calculate the diffraction of the wave you would need the wavelength and the
size and shape of the object or opening. If the ratio of the wavelength and
area is large then the sound waves would be more dispersed and spread out.
The
intensity of a sound wave is the power of the wave over the area that it
covers. The intensity of can be measured in decibels (dB). Decibels are based
on a logarithmic scale. The bigger the area that the sound wave travels, the
lower the intensity would be. Humans have very good hearing and can hear very
low intensities. They can detect an intensity as low as 1*10-12 W/m2.
The lowest point of intensity which humans could hear is known as the threshold
of hearing.
Works
Cited:
Hecht,
"Phase." Dictionary.