Lyceum A - Physics - Week 16 - Sound
- Mar 22, 2022
- 6 min read
Updated: Aug 24, 2022
Sound is caused by an object vibrating rapidly. This vibration causes the medium around it (water, air, etc) to vibrate in turn, thus sending out waves of sound that reach our ears.
There are speaker systems that are built to be used underwater. The sound waves emitted by these speakers cause the water to vibrate and you can hear the music under the water.
————————
Experiment:
Stretch a piece of plastic wrap across the opening of a bowl and fasten it ins place with a large rubber band. Sprinkle a few grains of sugar on top of the plastic.
Now take a big pot or pan and hold it near the bowl. Strike it with a spoon a few times. The grains of sugar will jump every time you strike the pot because the striking of the pot causes vibrations of the metal pot which then causes the air next to the pot to vibrate and that wave of air vibrating outward hits the plastic wrap which moves in response causing the sugar grains to move in response.
————————
In physiology, sound is produced when an object’s vibration move through a medium until the enter the human eardrum. In physics, sound is produced in the form of a pressure wave. When an object vibrates, it causes the surrounding air molecules to vibrate, initiating a chain reaction of sound wave vibrations throughout the medium. While the physiological definition includes a subject’s reception of sound, the physics definition recognizes that sound exits independently of an individual’s reception. - pasco.com
These vibrations travel in waves. Sound waves are much slower than light waves.
From ie.ac.uk:
The vibrating sound source moves in such a way that the air around it is also made to move. Imagine a drum skin being hit hard with a beater. The skin moves to one side and squashes or compresses the air next to it. This compressed air “pocket” in turn pushes and compresses the air next to it while the “pocket” itself bounces back towards the position it came from. The compressing effect and stretching effect therefore moves outward from the sound source. The movement of the air back and forth is itself a rapid vibration and the movement of the effect outwards is in a wave form. Eventually the effect reaches the ear and is made into signals which are sent to the brain.
Sound vibrations, then travel outwards in all directions in waves from a sound source. As they travel outwards the energy they contain becomes dissipated and therefore the sound becomes weaker the further it is from the source.
Figure 1 shows the air as particles or molecules. Where the molecules are pushed closer together is an area of compression and when they spring back (even further apart than before) there is an area of rarefaction. It can be seen that while the wave of compressed molecules moves away from the source, the molecules themselves only move a short distance to and fro. Thus, the air does not flow from the source to the ear-an idea often held by children.
A very good way of demonstrating how the molecules of a substance behave when transmitting a sound is to use a “slinky” spring extended on a desk surface. Push one end rapidly and a wave is sent along the length of the spring. It is possible to see the wave bounce back (an echo) and of course to see that the parts of the spring (representing the molecules) do not move along with the wave, but merely “vibrate” back and forth.
Slinkys and Soundwaves
National Music Centre - 2.18min
Sound waves are called longitudinal waves because the particles move back and forth in the direction of the wave movement. A transverse wave is like a wave on the sea in which the particles of water move vertically and not in the direction of the wave itself. For this reason it is a good idea to avoid likening a sound wave to the ripples on a pond.
Sound needs a medium in which to travel. Sound waves cannot form unless there are molecules to bump into each other to pass the wave form along. Sounds will therefore not travel in space where only a vacuum exists. You may have seen a classic demonstration in which an electric bell is enclosed in a glass bell jar. As the air is slowly pumped out of the jar the ringing bell is seen to be still moving , but the sound gradually diminishes until it can not be heard at all. Astronauts working in space or on the surface of the moon can therefore only talk to each other by using radio communication.
Sound can travel through matter, whether that matter is solid, gas or liquid.
The Transmission and Reflection of Sound - iitutor.com - 5 min
--------------------------------
Qualities of Sound:
Pitch - pitch is the frequency of a sound wave. Pitch can be high or low. Faster vibrations produce a higher pitch. Slower vibrations produce a lower pitch.
Intensity - Intensity is the amplitude of the sound wave. Intensity can be a degree of loudness or a degree of quietness.
————————-
What is Sound? - SciShow Kids - 3.57min
————————-
Humans make sounds by pushing air from their lungs over the vocal folds (vocal cords) in their larynx (voice box). This causes the vocal folds to vibrate which produces sound. The muscles of the larynx adjust the length and tension of the vocal folds to fine tune pitch and tone.
Tone is the use of pitch in language to distinguish lexical or grammatical meaning - that is, to distinguish or to inflect words. All verbal languages use pitch to express emotional and other paralinguistic information and to convey emphasis, contrast, and other such features in what is called intonation, but not all languages use tones to distinguish words or their inflections, analogously to consonants and vowels. Languages that do have this feature are called tonal languages; the distinctive tone patterns of such a language are sometimes called tonemes, by analogy with phoneme. Tonal languages are common in East and Southeast Asia, the Pacific, Africa, and the Americas; as many as seventy percent of world languages may be tonal. - wiki
We use our tongue, palate, cheeks, lips, etc. to articulate and filter the sounds coming from the larynx.
The vocal folds, in combination with the articulators, are capable of producing highly intricate arrays of sound. The tone of voice may be modulated to suggest emotions such as anger, surprise, fear, happiness or sadness. The human voice is used to express emotion, and can also reveal the age and sex of the speaker. - wiki
—————————
Longer, thicker vocal cords create lower, deeper voices.
Before puberty, your larynx sits higher in the neck. As you go through puberty, the larynx grows and moves lower in the neck. The vocal folds also thicken and enlarge. The change in pitch is much more dramatic in boys whose voice can drop about an octave lower while girls’ voices only drop about three tones. This process takes about a year before the voice stabilizes.
Ted Talks - Why does your voice change as you get older - video - 3.53 min
———————————-
Experiment:
Try making a few instruments that make musical sounds.
Kazoo: One empty toilet paper roll
Make a hole in the middle of the paper roll tube with a paper punch.
Place a piece of wax paper over one end of the tube and hold it in place with a rubber band.
To make the kazoo work you place your mouth at the open end and hum with the object to send the vibrations to the wax paper. The wax paper causes the sound to increase in loudness as the wax paper also vibrates along with the voice.
Drum:
Fill a pint or quart glass jar half full of water. Close the lid tightly.
Hold the container in your hand so that both ends are free.
Tip the jar so that the water starts a wave in the jar.
Hit the glass end of the jar with the fingers of your other hand to send vibrations through the water to make drum sounds.
String Instrument:
This experiment will create a sound like a herd of elephants.
Punch a hole in the base of a paper cup just large enough to slip a long length of sting into the cup and tie a knot onto a paper clip.
Pull the string taunt. Soak the string with water.
Hold the cup with one hand and with the fingers of the other hand firmly hold the string near the base of the cup and pull you finger down the length of the string. (If it doesn’t work, wet the string more and practice again)
Sound Making Cup - Michael DiSpezio - 3.09min
We are using friction to produce vibrations in this case. The friction causes energy to heat up the atoms causing them to vibrate which produces sound.
Comments