Sound 3/27/15

Big Waves Video Big Waves: Ct1U&feature=related Ct1U&feature=related

Sound Sound: Vibrations transmitted through a solid, liquid or gas. Vibrating an object vibrates the medium (air) that transports the sound. Sound is a longitudinal pressure wave.

Sound Compression: A pulse of high pressure air Rarefaction: A pulse of low pressure air

Sound Waves Still have the 4 wave parts: – Wavelength – Amplitude – Crests (Compression) – Troughs (Rarefaction) 5

Sound Intensity Decibel: Loudness of sound, a unit for measuring the intensity or energy of a sound (dB) Pitch: The frequency of sound

Beats Beats: A variation in loudness of sound caused by interference of tones Tones need to be within 10 Hz of each other

Human Hearing Frequency Range 20 Hz to 20,000 Hz Infrasonic: Sound pitch below 20 Hz, too low to be heard by the human ear Ultrasonic: Sound pitch above 20,000 Hz, the upper limit of human hearing

Doppler Effect Doppler Effect: The change in frequency of a wave due to the motion of the source or of the receiver

New Equations Period and Frequency Wave Velocity Sound Intensity 11

Example - Waves Assuming the speed of sound in air is 345 m/s. What if the frequency of a sound wave with a wavelength of 1.10 m? 12

Example – Sound Intensity When there are no students in the classroom the sound level is 42.1 dB. When the bell rings the sound level is 78.4 dB. How many times louder is it when the bell rings? H.W. “Sound and Waves” W.S. due Mon. (3/30/15)

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Letters for August The letters should include: Favorite labs, activities, demos or projects Advice about how to be successful in physics Letters should be positive Designed to help calm students’ jitters about taking physics Letters will be used for next year, but will be kept anonymous (use an alias) Needs to be at least a page long Some will be filtered

Doppler Effect

Sound Levels Threshold of Hearing 0 dB Normal Breathing 10 dB Whisper 20 dB Refrigerator Humming 40 dB Normal Conversation 60 dB Busy Traffic 80 dB Lawn Mowers 100 dB Rock Concert 110 dB Threshold of Pain 120 dB Jet Engine130 dB

Hearing Damage Sound Level in dBDuration 908 Hours 954 Hours 1002 Hours 1051 Hour Min Min Min Can cause immediate damage

Hearing Loss Tinnitus Sound Level – dB Pitch Range

Hearing Loss Threshold of Hearing 0 dB Normal Breathing 10 dB Whisper 20 dB Refrigerator Humming 40 dB Normal Conversation 60 dB Busy Traffic 80 dB Lawn Mowers 100 dB Rock Concert 110 dB Threshold of Pain 120 dB Jet Engine130 dB Threshold Of Hearing

Hearing Loss Frequency Range 20 Hz to 20,000 Hz This range becomes narrower.

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Doppler Effect Videos -

Doppler Effect