Sound Production and Propagation

• Sound helps humans communicate and experience the environment
• Sounds of musical instruments are heard in a school's music room

Sound Production

• Sound is produced by a vibrating body
• The back and forth movement of an object is called vibration
• When vibration stops, sound stops

Sound Can Propagate Through Solids, Liquids And Gases

Activity Examples

• Striking a metal plate or pan causes vibrations and sound
• Sound production requires vibration
• Plucking a stretched rubber band causes it to vibrate and produce sound
• Waves are visible on the surface of water in a dish when the dish is struck
• Sound has a connection with the vibrations of a body
• Musical instruments like the Veena and Tabla produce sound from stretched strings or membranes
• Instruments like the Manjira, Ghatam, Noot and Kartal are beaten or struck to create sound

Human Sound Production

• In humans, the voice box or larynx produces sound
• Vocal cords stretch across the voice box with a narrow slit for air passage
• Air from the lungs vibrates the vocal cords, producing sound
• Muscles adjust vocal cords for different sounds
• Vocal cords are about 20 mm long in men and 15 mm long in women thus the sounds are different

Sound Travels Through a Medium

• Sound propagates or travels to be heard
• Sound requires a medium and can travel through solids, liquids and gases
• Sound cannot travel through a vacuum
• Whales and dolphins communicate underwater

Hearing

• The outer ear is shaped like a funnel
• Sound travels down a canal to a thin stretched membrane called the eardrum
• The eardrum vibrates and sends signals to the brain
• The number of oscillations per second is the frequency of oscillation, measured in hertz (Hz)
• A frequency of 1 Hz means one oscillation per second
• Amplitude and frequency differentiate sounds

Loudness of Sound

• Loudness is proportional to the square of the amplitude
• Loudness is measured in decibels (dB)
• Normal breathing is 10 dB
• A soft whisper is 30 dB
• Normal conversation is 60 dB
• Busy traffic is 70 dB
• An average factory is 80 dB
• Sounds above 80 dB can be physically painful

Pitch Of Sound

• Frequency determines the shrillness or pitch of a sound
• Higher frequency equates to a shrill sound with a higher pitch
• Lower frequency equates to a sound with a lower pitch
• A bird's high-pitched sound differs from a lion's low-pitched roar
• Woman's voice has a higher frequency than a man's

Audible Range

• Sounds less than 20 Hz are inaudible to the human ear
• Sounds higher than 20,000 Hz are also inaudible to the human ear
• The audible range for humans is roughly 20 to 20,000 Hz
• Some animals, like dogs, can hear frequencies higher than 20,000 Hz

Noise and Music

• Unpleasant sounds are considered noise
• Musical sound is pleasing to the ear
• Loud musical sound become noise

Noise Pollution

• Excessive or unwanted sounds in the environment is noise pollution
• Causes include vehicles, explosions, machines, and loudspeakers
• Home sources contributing to noise pollution include televisions, radios, kitchen appliances, desert coolers and air conditioners

Harm of Noise Pollution

• Excessive noise can cause health problems
• Health problems can include: lack of sleep, hypertension, anxiety, and temporary or permanent hearing impairment

Noise Pollution Reduction

• Silencing devices should be installed in engines, vehicles, industrial machines, and home appliances
• Noisy operations should be away from residential areas
• Noise producing industries should be set up away from residential areas
• The use of automobile horns should be minimized
• TV and music systems should be run at low volumes
• Plant trees along roads and around buildings
• Trees cut down on sounds, reducing the harmful noise effects
• Hearing impairment can be from birth, disease, injury or age
• Sign language can help kids communicate effectively and overcome hearing loss