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