Unit 2Sound

Physical ScienceMrs. Lewis

How sounds are made

• Produced when matter vibrates

• Travel as longitudinal wave and mechanical wave

Frequency = Pitch• Pitch is a description of how high

or low a sound is• Depends on the

frequency/wavelength• High frequency is high pitch• Normal human hearing range is

20-20,000 Hz• Ultrasonic is higher than 20,000 Hz• Infrasonic is lower than 20 Hz

Loudness

• Loudness is measure of how well a sound can be heard

• Indicated by amplitude of a wave• Unit of volume is decibel (dB)• Sounds > 120 dB are painful

Doppler Effect• Definition is change in

observed frequency of a

wave when the sound source, the observer, or both are moving

• Apparent increase in pitch as movement is towards sound, decrease in pitch when movement is away

Speed of Sound – Depends on Medium

• Phase – Fastest through solids, slower through

liquids, slowest through gases

• Temperature– Lower temp = slower speed/Higher

temp = faster speed– Because molecules move

slower/faster

Interaction of Matter & Sound

• Reflection – Bouncing back of a wave when the

wave hits a barrier (echo)– Sound waves reflect best off smooth

hard surfaces

• Absorption– Rough wall absorbs sound better

Sonar

• Stands for Sound Navigation and Ranging

Uses for SONAR

• Commercial fishing• Mapping ocean floor• Camera that focuses automatically• Bats/dolphins• Cars

Ultrasound

• Ultrasonic Cleaning (15-400 kHz)• Jewellery, lenses, coins, watches, dental and surgical

instruments, fountain pens, industrial parts, electronic equipment, cellular phone repair

• Industrial ultrasonic cleaners are used in the automotive, sporting, printing, marine, medical, pharmaceutical, electroplating,

engineering and

weapons industries

Medical Uses

• Unborn baby• Allow doctors to see inside body• Destroy unwanted tissues• Physical therapy to heat injured

muscles

Ultrasound of baby

Interactions of Sound Waves• Interference – when two or more

waves overlap and combine to form one wave

• Constructive interference– Waves combine to form a wave with a

larger amplitude (sonic booms)

• Destructive interference– Waves combine to form a wave with a

smaller amplitude (noise canceling headphones)

Resonance• Happens when a sound wave matches

the natural frequency of an object and causes the object to vibrate

• Natural frequency – all objects have a frequency (or set of) that it vibrates at

Resonance

• Musical Instruments– Air into mouthpiece cause vibration– Vibrations form standing wave & get

louder– Standing wave is pattern of vibration

that looks like a wave is standing still– Resonance occurs when standing wave

is formed