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Sound produced by humans happens due to a voice box called larynx. In the throat, at the top of the windpipe a voice box is situated. Sound gets generated when vibration is made by a material. Similarly, when vocal cords vibrate, sound is produced. Vocal cord is attached to muscles of the throat and when they get relaxed completely, vocal cords are separated. Due to this, air (from lungs) will pass through them without producing sound. When humans don't talk or sing, two vocal cords are away from each other with some gap.
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Key Terms: Amplitude, eardrum, hertz (Hz), voice box or larynx, loudness, oscillatory motion, oscillation, pitch, shrillness
Also read: Difference Between Larynx and Pharynx
Vibrating Body
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Vibrating body produces sound. All that you can hear, speech, music from television, music from the instrument, the sound of rain, etc. all is produced by the vibration of different bodies.
Activity 1.2
Take a metal plate or frying pan. Hang it with a string such that it does not touch any wall. Place your finger on the plate. Strike the plate with a wooden stick such that it produces sound. Place your hand on the plate while it is producing sound. You will feel vibrations. Again strike the plate with the wooden stick. This time tightly holds the plate while it is producing sound. It will tend to stop producing sound as the tightness of your hands will restrict the plate to vibrate.
Activity 1.3
Take a metal container and fill some water in it and strike it with a spoon at the edge. Sound will be produced. Do the same and feel the container with your hands. You will feel the vibrations. Not only that, you will see some waves on the water. Strike the container the third time, this time while holding the container in your hands. You will see a fewer number of waves on the water as you are holding a container and hindering it from vibrating. This is a visual which connects the sound with the vibration.
Activity 1.4
You can also make another instrument called Jaltrang. It is easy to make as it requires only 6-8 bowls or tumblers. Fill them up with the different amounts of water increasing gradually from one side to the other. Now take a stick and strike the tumblers in successions. You will hear different sounds pleasant to ears. Different sounds are produced because of different amounts of water in tumblers.
Explanation of Given Activities
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- Vibration is to and fro or back and forth motion of an object.
- When a tightly stretched string is plucked or a metal object is struck by a stick, it starts vibrating and produces sound.
- Noot, a musical instrument, also called mudpot, which seems to be stiff, vibrates when we strike it with our hands.
- Musical instruments like table, veena are simply beaten or struck.
- When we pluck strings of an instrument like a sitar, the whole instrument vibrates, it is not only the sound of the string that vibrates to produce such a musical sound.
- In flute (bansuri), the air is made to vibrate. Vibration of the air produces a relaxing and soothing sound.
Also read: Beats
Sound Produced by Humans
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Human body has an organ called a voice box or larynx which is responsible for producing sound. Find a part of you which seems to move up and down when you swallow food. This part is known as the voice box or larynx. It is just above the windpipe. Two vocal cords are stretched across the larynx or voice box in such a way that it leaves a narrow path between for passage of air. When air from the lungs forces its way through this path, vocal cords vibrate and produce sound.
Muscles attached to vocal cords make the cords tight and loose. This flexibility gives us the ability to produce different sounds easily. For instance, when vocal cords are tight and thin, the quality of voice is different than when the vocal cord is loose and thick.
These vocal cords also decide different textures of sounds. Vocal cords in men are 20 mm long while in women they are about 5 mm long. Children have much shorter vocal cords. This is why we can differ between the sounds of men, women, and children.
Activity 3.1
Take a piece of paper. Make a small hole in it. Fold it from the hole such that the hole gets divided. Now hold it in your hands as shown. Blow air through this hole (narrow slit). You will hear sound. Our vocal cords work similarly.
Medium of Propagation
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Unlike light, sound needs a medium of propagation. It means sound cannot travel in a vacuum. You can hear your friend talking from a distance because sound travels from his mouth through the air to reach your ears. In the absence of air, you will hear nothing. To understand sound propagation in a medium, perform the following activities.
Activity 4.1
Take a dry metal or glass tumbler. Place a cell phone in it and ask a friend or a family member to give a call on the cell phone. Now place your hand on it such that no air passes and place on call on it again.
The loudness of sound coming out of the glass will decrease. Repeat the experiment by placing your mouth on the opening of the glass in such a way there is no exchange of air and such out all the air from glass. You will hear while sucking the ringing sound of the air gets even lower. This is because gas inside the glass decreases and the medium for the sound to travel outside keeps decreasing.
Activity 4.2
To test if water can also be a medium for sound to propagate, carry out this activity. Have a bucket or bathtub filled with water. Take a small bell in your hand. Dip this bell in water and shake it. Now get your ear close to the surface of the water, water should not enter your ear. The sound of the bell you will hear will indicate that sound can also travel through water. This is the reason also why dolphins and whales can communicate underwater.
Activity 4.3
Take a meter scale or a long rod. Hold one end near your ear and ask someone to scratch or rub the other end. You will feel the sound of scratching traveling from one end to the other. You can also perform this experiment differently. Place your head on the table such that your ear touches the surface of the table. Ask your friend to knock or scratch at the end of the table. You will feel sound traveling from the end to you through this wooden or metallic table. This observation shows that sound can also travel through solids.
Thus, we can conclude that sound needs a material medium to travel or propagate. It travels in all directions in a medium. Sound cannot travel through a vacuum but it can easily be transmitted through air, water, or any kind of solid. It can also travel through strings.
How Do We Hear a Sound?
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Sound is heard through our ears. Every kind of sound enters through our ears. The outer part of the air is shaped like a funnel. When the sound enters our ear, it goes through a canal at the end where a thin membrane is stretched tightly. This thin membrane is called eardrum.
Activity 5.1
Take a plastic or tin can. Cut both ends so that it has an opening from the sides. Take a rubber balloon and stretch it across one end of the can and tighten it with a rubber band. Put four or five grams of cereal on it. Shout ‘Hurray, Hurray’ through it. You will see the cereals bouncing up and down.
Eardrum is like a stretched rubber balloon. It vibrates according to the sound produced. From the eardrum, vibrations travel to the inner ear. From there, the signal is transmitted to the brain. Brain decodes this signal and that’s how we hear.
Things to Remember
- The vibration of vocal cords in humans is the key reason for the sound produced by humans
- Sound needs a material medium to travel, be it gas, liquid or solid. It just cannot travel through a vacuum.
- Vibrations of sound are felt by eardrums which in turn send the signal to the brain. The process is known as hearing.
- Frequency is described as the number of oscillations or vibrations per second.
- Unit of frequency is hertz (Hz).
- Loudness of sound is directly proportional to the amplitude of vibration.
- Frequency of vibration is directly proportional to the pitch of the sound. Higher the pitch, shriller the sound.
- Different sounds can be identified because they have different frequencies.
Also read:
Sample Questions
Ques. What is the voice box or larynx? Explain its function with a diagram. (3 Marks)
Ans. The voice box or larynx is an organ in the human body that is responsible for producing sound. It is located just above the windpipe. Two vocal cords are stretched across the larynx or voice box in a way that they leave a narrow path between for passage of air. When air from the lungs forces its way through this path, vocal cords vibrate and produce sound. Vocal cords have muscles that make them tight or loose. This flexibility produces high and low-pitched sounds.
Ques. Why do men, women, and children sound different? (2 Marks)
Ans. Vocal cords decide different textures of sounds. Vocal cords in men are 20 mm long while in women they are about 5 mm long. Children have much shorter vocal cords. Since the size of the vocal cords differ, how they vibrate also differs. Different vibration means different sound. This is why we can differ between the sounds of men, women, and children
Ques. Why can't sound travel in a vacuum? Also, list down some materials through which sound can travel. (2 Marks)
Ans. Sound requires a material medium through which it can propagate, be it air, liquid or solid. In a vacuum, there is an absence of all three, sound has no medium to propagate through. So, in vacuum humans are unable to hear anything.
Sound can travel through all kinds of materials. It just cannot travel through a vacuum. So, air, any liquid be it water, wood, book, string, wires, plastic, ground, etc. are all examples of the medium through which sound can travel.
Ques. Define frequency? Also, write its units. (1 Mark)
Ans. The number of to and fro motions per second is called the frequency of oscillation. Frequency is measured in hertz. The symbol used is Hz.
Ques. How is loudness related to the amplitude of vibration? Write the units of loudness. (2 Marks)
Ans. Loudness of sound is directly proportional to the square of the amplitude of the vibration. This means the higher the amplitude, the higher will be the loudness. If the amplitude becomes 3 times, the loudness will become 9 times. We can measure loudness by a unit called the decibel. Its symbol is DB.
Ques. What is eardrum? Explain with a diagram. (2 Marks)
Ans. Eardrum is a part of the ear. Sound is detected by the human body through eardrums. It is a sensitive part, as the sound falls on it, it starts vibrating and sends it to the inner part of the ear.
Ques. How is pitch related to the frequency of vibration? Explain with an example. (2 Marks)
Ans. Higher the amplitude of vibration, the higher will be the pitch. Although the song of a bird has a higher pitch (higher frequency) while the roar of a lion has a lower pitch (lower frequency), the loudness of a roar is more than that of a song.
Ques. What factor helps us to differentiate between two sounds which have the same loudness? (2 Marks)
Ans. The frequency of vibration is the factor by which we can easily differentiate between two sounds because the frequency is directly related to the pitch or shrillness of the sound. This is why we can also differentiate between songs.
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