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Sound
Importance of Sound
- Daily Life Examples:
- Knowing a school period is over by the bell.
- Hearing a knock or doorbell to know someone is at the door.
- Identifying someone approaching by their footsteps.
- Blind-folded person in hide and seek guessing who’s nearby by sound.
- Role of Sound:
- Essential for communication.
- Surroundings filled with various sounds.
Activity:
- Make a list of sounds you hear around you.
- In the music room, you hear sounds from instruments like flute, tabla, harmonium, etc.
Sound is Produced by a Vibrating Body
- Observation:
- Touch a school bell when not in use and when it is ringing. Feel the vibrations.
- Vibration:
- To and fro/back and forth motion of an object.
- Example: Plucking a tightly stretched band makes it vibrate and produce sound.
- No vibration, no sound.
- Musical Instruments:
- List instruments and identify their vibrating parts. (e.g., sitar, mridangam).
- Instruments like manjira, ghatam, kartal produce sound by being struck.
- Interesting Fact:
- The whole instrument vibrates when played, not just the strings or membranes.
Sound Produced by Humans
Activity:
Speak, sing, or buzz like a bee and feel your throat. Notice the vibrations.
Voice Box (Larynx):
- Voice Box (Larynx):
- Located at the upper end of the windpipe.
- Contains two vocal cords with a narrow slit for air passage.
- Vibrations of vocal cords produce sound.
- Vocal Cord Tension:
- Muscles adjust the tightness of the vocal cords.
- Tight and thin vocal cords produce a different voice quality compared to loose and thick ones.
Fun Fact
- Vocal Cord Lengths:
- Men’s vocal cords: ~20 mm.
- Women’s vocal cords: ~15 mm.
- Children’s vocal cords are shorter, hence different voice tones.
Sound Needs a Medium for Propagation
How Sound Travels
- When you call a friend standing at a distance, your voice reaches them through the air.
Activity 10.7: Sound and Air
- Materials Needed: Metal or glass tumbler, cell phone
- Steps:
- Place a cell phone in a dry tumbler.
- Have a friend call the cell phone and listen to the ring.
- Cover the rim of the tumbler with your hands and put your mouth on the opening.
- Have your friend call again and listen while sucking air from the tumbler.
- Notice if the sound becomes fainter as you suck air.
- Remove the tumbler from your mouth and see if the sound becomes loud again.
- Explanation:
- The loudness decreases as the air is sucked out because sound needs air (a medium) to travel.
- In a vacuum (no air), sound cannot travel.
Sound in Different Mediums
Activity 10.8: Sound in Liquids
- Materials Needed: Bucket or bathtub, clean water, small bell
- Steps:
- Fill the bucket/tub with water.
- Shake a small bell underwater without touching the sides.
- Place your ear gently on the water surface and listen.
- Observation:
- You can hear the bell, indicating that sound can travel through liquids.
- Interesting Fact:
- Whales and dolphins communicate underwater using sound.
Activity 10.9: Sound in Solids
- Materials Needed: Metre scale or long metal rod
- Steps:
- Hold one end of the scale/rod to your ear.
- Have a friend scratch or tap the other end.
- Check if you can hear the sound.
- Observation:
- Sound can travel through solids like wood and metal.
- Example: Making a toy telephone using strings shows that sound can travel through strings.
Summary
- Sound needs a medium (gas, liquid, or solid) to travel.
- It cannot travel through a vacuum.
We Hear Sound through Our Ears
How Ears Work
- Outer Ear:
- Shaped like a funnel to catch sound waves.
- Directs sound down a canal to the eardrum.
- Eardrum:
- A thin, stretched membrane that vibrates with sound.
- Sends vibrations to the inner ear, then to the brain, allowing us to hear.
Activity 10.10: Eardrum Model
- Materials Needed: Plastic or tin-can, rubber balloon, rubber band, dry cereal grains
- Steps:
- Cut the ends of the can.
- Stretch the balloon piece over one end and secure with a rubber band.
- Place grains on the stretched balloon.
- Have a friend speak into the open end and observe the grains.
- Observation:
- The grains jump up and down, showing the vibrations caused by sound.
- Safety Tip:
- Never insert sharp or hard objects into your ear to avoid damaging the eardrum.
Amplitude, Time Period, and Frequency of a Vibration
Understanding Vibrations
- Vibration/Oscillatory Motion:
- To and fro motion of an object.
- The number of oscillations per second is called frequency (measured in Hertz, Hz).
- Example:
- An object oscillating 20 times in one second has a frequency of 20 Hz.
Properties of Sound
- Amplitude and Frequency:
- These determine the characteristics of sound.
- Amplitude affects loudness.
- Frequency affects pitch.
Loudness and Pitch
Activity 10.11: Exploring Sound
- Materials Needed: Metallic tumbler, tablespoon, small thermocol ball
- Steps:
- Gently strike the tumbler with a spoon and listen to the sound.
- Strike the tumbler harder and listen again.
- Suspend a thermocol ball touching the tumbler’s rim and strike the tumbler.
- Observations:
- The ball’s displacement shows the amplitude of vibrations.
- Harder strikes result in larger amplitudes and louder sounds.
Understanding Loudness
- Loudness:
- Depends on the amplitude of vibrations.
- Larger amplitude = louder sound.
- Smaller amplitude = feeble sound.
Understanding Pitch
- Pitch:
- Depends on the frequency of vibrations.
- Higher frequency = higher pitch (e.g., whistle, bird sounds).
- Lower frequency = lower pitch (e.g., drum, lion’s roar).
- Examples:
- A child’s voice has a higher frequency than an adult’s.
- A woman’s voice usually has a higher frequency than a man’s.
More to Know
- Loudness and Amplitude Relationship:
- Loudness is proportional to the square of the amplitude.
- Example: Double the amplitude increases loudness by four times.
- Loudness is measured in decibels (dB).
- Examples of Loudness:
- Normal breathing: 10 dB
- Soft whisper: 30 dB
- Normal conversation: 60 dB
- Busy traffic: 70 dB
- Average factory: 80 dB
- Above 80 dB: Noise becomes physically painful.
Audible and Inaudible Sounds
- Audible Range:
- Human ears can hear sounds between 20 Hz to 20,000 Hz.
- Sounds below 20 Hz and above 20,000 Hz are inaudible to humans.
- Interesting Facts:
- Dogs can hear sounds above 20,000 Hz.
- Police use high-frequency whistles that only dogs can hear.
- Ultrasound equipment operates at frequencies higher than 20,000 Hz, useful in medical investigations.
Noise and Music
Different Types of Sounds
- Pleasant and Unpleasant Sounds:
- Not all sounds are pleasing.
- Unpleasant sounds cause discomfort and are called noise.
- Examples: Sounds from construction sites, horns of buses and trucks.
- Classroom Noise:
- When all students speak together, the sound is noise.
- Musical Sounds:
- Pleasing to the ear.
- Examples: Sounds from a harmonium or sitar.
- Loud musical sounds can become unpleasant.
Noise Pollution
What is Noise Pollution?
- Definition:
- Presence of excessive or unwanted sounds in the environment.
- Sources of Noise Pollution:
- Vehicles, explosions, machines, loudspeakers.
- Home sources: Loud TV, radio, kitchen appliances, air conditioners.
Harms of Noise Pollution
- Health Problems:
- Lack of sleep, high blood pressure, anxiety.
- Continuous loud sounds can cause temporary or permanent hearing loss.
Measures to Limit Noise Pollution
- Controlling Noise Sources:
- Install silencing devices in engines, vehicles, machines, home appliances.
- Conduct noisy operations away from residential areas.
- In Residential Areas:
- Minimize use of automobile horns.
- Keep TV and music volumes low.
- Plant trees along roads and buildings to reduce noise.
More to Know
- Hearing Impairment:
- Total hearing impairment is rare and usually present from birth.
- Partial hearing loss can result from disease, injury, or age.
- Special care needed for children with hearing loss, including learning sign language.
- Technological devices can improve the quality of life for the hearing-impaired.
- Society can help by creating a better environment for the hearing-impaired.
Chapter Summary:
- Sound is produced by vibrating objects.
- In human beings, the vibration of the vocal cords produces sound.
- Sound travels through a medium (gas, liquid, or solid).
- It cannot travel in a vacuum.
- The eardrum senses the vibrations of sound.
- It sends the signals to the brain.
- This process is called hearing.
- The number of oscillations or vibrations per second is called the frequency of oscillation.
- The frequency is expressed in hertz (Hz).
- Larger the amplitude of vibration, the louder is the sound.
- Higher the frequency of vibration, the higher is the pitch, and shriller is the sound.
- Unpleasant sounds are called noise.
- Excessive or unwanted sounds lead to noise pollution.
- Noise pollution may pose health problems for human beings.
- Attempts should be made to minimize noise pollution.
- Plantation on the roadside and elsewhere can reduce noise pollution.
KEYWORDS
- AMPLITUDE
- EARDRUM
- FREQUENCY
- hertz (Hz)
- LARYNX
- LOUDNESS
- NOISE
- OSCILLATION
- PITCH
- TIME PERIOD
- VIBRATION
- VOICE BOX
- WIND PIPE
