Sounds study guide

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Sounds study guide

How sound is produced:

As an object vibrates it gives off energy to the particles of matter around it.
These vibrations travel through air in a series of rarefactions and compressions (a longitudinal wave)
Sound is produced as the matter vibrates and travels as a longitudinal wave
A medium is required for sound to be heard.

Speed of Sound

The speed depends on the properties of the medium. Sound can travel through any medium (solid, liquid or gas).
Speed of sound in air: 340 m/sec.
Speed of sound in ground: 1490 m/sec.
Determined by the temperature, elasticity and density of the medium through which the sound travels.

Properties

Temperature: Sound travels slower at low temperatures
Elasticity (ability to rebound): The more elastic the medium the faster the sound. Solids are more elastic than liquids or gases.
Density: The more dense the medium the slower the sound travels, its particles do not move as fast

What is sound?
What kind of wave carries sound?
What characteristics of the medium affects the speed of sound?
Compare the transmission of sound in solids, liquids and gases.

Pitch

Pitch: description of sound as high or low, depends on how fast the particles of the medium vibrate in a given time (the frequency) so… the pitch depends on the frequency of the waves.
High frequency = high pitch
Low frequency = low pitch

Doppler Effect: Change in pitch of a moving object as it comes towards and moves away from you. (NASCAR, Siren) High pitch as they move toward you and low pitch as they move away from you.

Frequency

1 hertz = 1 wave (1 complete rarefaction and compression)
Humans hear from 20 to 20,000 hertz
Ultrasonic: frequencies higher than 20,000 hertz; examples: dogs, cats, porpoises, bats
Infrasonic: Frequencies lower than 20 hertz; examples: elephants, earthquakes, volcanoes, machinery

Loudness

Loudness is related to the amount of energy carried by a wave
Intensity: determines the loudness of a sound. Defined as the amount of energy in a certain time, relates to amplitude
Amplitude: the larger the amplitude the greater the intensity
Decibel: scale in which intensity is judged.
0 dB = no sound, thunder is 120 dB, sounds with a dB of greater than 120 can cause pain in humans, 85 dB can cause ear damage

What characteristic of sound is determined by frequency? By amplitude?
Compare ultrasonic and infrasonic waves.
Describe the Doppler effect.

Review of Wave Energy

What happens when two crests meet?
What happens if the crest of one wave meets the trough of another?
Where would you want to hear perfect sound with no interference?
What happens when you put carpet in a room?

Sound quality

Music: when sound has a pleasing quality, a definite identifiable pitch and a repeated timing called rhythm.
Noise: has no pleasing qualities, no pitch and no rhythm. Examples include chalk on the chalkboard, jackhammer, baby crying
Acoustics – the science of sound. Scientists in this area design “perfect” concert halls and auditoriums.
Each instrument has its own sound quality or timbre.

Applications of sound

Sonar: when sound waves are sent in a straight line down until it reaches a barrier and is reflected back. Used for fishing, to find oil, mapping
Ultrasonic Cleaning: waves are used to clean jewelry, electronic components, machine parts. Sound waves are sent through a liquid where it vibrates causing dirt to be knocked off the object
Ultrasound: sound wave sent through body and an image is drawn showing body part, can also be used to treat cancer and is used in physical therapy for injured muscles

How you hear

Sound waves enter the outer ear
Move through ear canal and strikes the eardrum which vibrates like a drum
Vibrations enter the middle ear and hits the hammer, anvil and then the stirrup
The vibrations then travel to the liquid filled inner ear
Vibrations enter the cochlea (looks like a snail) which contains cells that attach to nerves which lead to the brain where they are interpreted as sound.

Where does hearing begin in humans?
What are three main parts of the ear?
What is the function of the eardrum?
Where are nerve impulses interpreted as sound?
Sometimes loud sounds can actually tear your eardrum. What characteristic of a sound wave causes the injury?
How do you think the injury affects hearing?

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