The Physics Of Sound

Objective: Explain the nature of sound waves and how they are produced

The Physics Of SoundWhy do we hear what we hear?

(Turn on your speakers)

1How are sound waves produced?Mechanical wavesSound energy requires matter in order to transport it

Sound Energy (pulses) create vibrations causing changes in pressure

2How are sound waves produced?A longitudinal wave caused by pressure fluctuations in vibrating objects: Compressions: high pressure regions (crowded area)Rarefactions: low pressure regions (relaxed area)Frequency- # of compressions passing/secondWavelength distance between compressionsA 3-dimensional arrangement

3What happens to the speed of sound in different types of matter (media)?Each substance transfers sound energy at a different rateThe rate is dependent on:

Tension - the higher the tension between molecules, the faster sound travels though a medium. thermal energy - higher the temperature, the faster the molecules move and allow sound to travel through medium.

4How do you break the sound barrier?Supersonic - an object moves faster than the speed of sound

Moving at the speed of sound is known as Mach 1Exceeding Mach 1 (the sound barrier) causes a shock wave known as a sonic boom Used to determine the speed of an aircraftWhat is meant by Mach 2, or 3 etc. ?

5What is a sound detector?Converts sound energy into other forms of energy.Allows humans to observe a sound wave Often converts a compression (longitudinal wave) into a electromagnetic wave (transverse wave)Ex. Microphone, the ear, ultrasonic machine

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How does the ear work as a sound detector?collects and directs sound

vibrates and send to the middle ear

Lever system that amplifies sound vibrations

Vibration of tiny hairs, transmitted to brain by nerves

8The three components of sound are:Pitch (how high or low)

Loudness (volume)

Timbre (tone color)

9What is the relationship between the frequency and pitch of a sound? Pitch is the highness or lowness of a sound perceived by humans The qualitative observation (how high or low)derived from the frequency

Frequency is the measurable quantityThe quantitative observationMeasured in Hertz The higher the frequency, the higher the pitch

10When the frequency of a sound doubles we say that the pitch goes up an octave.We can hear a range of pitches of about ten octaves.Many animals can make sounds and hear frequencies that are beyond what we can hear.

11What frequencies can humans hear?Human Range (audible)20 Hz - 20,000 HzWe hear best between 200 and 2000 HzChanges with age and damage to the earUltrasonic Anything above 20,000 HzUsed for sonar and medical diagnosisInfrasonic Anything below 20 HzHeavy machinery, lightning, elephantsWe might not hear it, but you may feel these12

13What are the audible frequencies of other organisms?Grasshopper 100 to 50,000Moth1000 hz 240,000 hzDog40 hz 46,000 hzCat 100 hz 60,000 hzMouse1,000 hz 91,000 hzBull frog 100 hz 3000 hzTree frog 50 hz 4000 hzChicken 125 hz 2,000 hzElephant 16 hz 12,000 hzCanary250 hz 8,000 hzBeluga whale 1000 hz 123,000 hzTuna 50 hz 1,100 hzOwl 20 hz 12,000 hzBat 2,000 hz 110,000 hzGerbil 100 hz 60,000 hzHippo 30 hz 64,000 hzFerret 16 hz 44,000 hz

14What is the relationship between the amplitude and loudness of a sound? Loudness is the volume a sound perceived by humans A qualitative measure of the power in a waveCan be quantified using decibelsderived from the amplitude

Amplitude is the measurable quantityThe quantitative observationMeasured in meters

The larger the amplitude, the more energy in a wave and the more powerful it is.15Loudness vs. DecibelSource of SoundDecibelsBoeing 747140Civil Defense Siren130Jack Hammer120Rock Concert110Lawn Mower100Motorcycle90Garbage Disposal80Vacuum Cleaner70Normal Conversation60Light Traffic50Background Noise40Whisper30For every increase in 10 Decibels, the loudness DOUBLES!TimbreHarmonicContent of sound

Attack and Decay of sound

VibratoPeriodic changes in the frequency/amplitude

The of sound.bendingDiffraction of Sound

Refraction of Sound

Daytime refraction of sound due to ground temperature being higher than air

Nighttime refraction of sound when ground cools off quickly but warm air from the day stay in the air.