Presentation on theme: "Chapter 10: Sound Section 1: The Nature of Sound"— Presentation transcript:
1 Chapter 10: Sound Section 1: The Nature of Sound Section 2: Properties of SoundSection 3: MusicSection 4: Using Sound
2 Section 1: The Nature of Sound Sound wavesAll sound waves are created by something that vibratesA stereo speaker:The vibrating diaphragm of the stereo speaker collides with nearby air molecules, transferring some energy to themThese molecule then collide with other molecules and pass the energy to themThe process of molecular collision and energy transfer form a sound waveA sound wave is a compressional waveRequires a medium through which to travelSound can travel through solids, liquids, or gasesThe speed of sound is different in different mediaSolids fast, liquids slower, gases slowestThe speed of sound in air varies with temperatureAt 0oC, Vsound = m/sAs the temperature increases, speed increasesAs temperature falls below 0oC, speed decreases
3 Section 1: The Nature of Sound The equation for speed of sound:Example 1: If the temperature is 15oC, what is the speed of a sound wave?SolutionWhere:V = speed of sound (m/s)T = change in temperature (from 0oC to actual temperature)use “+” if the temp. is greater than 0oCuse “-“ if the temp. is less than 0oCT = 15oCV = ?∆T= 15 o C − 0 o C∆T= 15 o C𝑉=331.5 𝑚 𝑠 ±0.6 𝑚 𝑠 𝑜 𝐶 ∆𝑇𝑉=331.5 𝑚 𝑠 +0.6 𝑚 𝑠 𝑜 𝐶 ( 15 𝑜 𝐶)𝑉=331.5 𝑚 𝑠 +9.0 𝑚 𝑠𝑽=𝟑𝟒𝟎.𝟓 𝒎 𝒔
4 Section 1: The Nature of Sound Example 2: What is the speed of sound when the temperature is –10oC? Solution Example 3: The temperature is 10oC, how far will a sound travel in 10.0-s?𝑇=− 10 0 𝐶𝑉= ?∆𝑇= 0 𝑜 𝐶 −(− 10 𝑜 𝐶)∆𝑇=10℃𝑉=331.5 𝑚 𝑠 ±0.6 𝑚 𝑠 𝑜 𝐶 ∆𝑇𝑉=331.5 𝑚 𝑠 −0.6 𝑚 𝑠℃ 10℃𝑉=331.5 𝑚 𝑠 −6.0 𝑚 𝑠𝑽=𝟑𝟐𝟓.𝟓 𝒎 𝒔𝑇=10℃𝑡=10.0𝑠𝑑= ?∆𝑇=10℃−0℃∆𝑇=10℃𝑉=331.5 𝑚 𝑠 ±0.6 𝑚 𝑠 𝑜 𝐶 ∆𝑇𝑉=331.5 𝑚 𝑠 +0.6 𝑚 𝑠℃ 10℃𝑉=331.5 𝑚 𝑠 +6.0 𝑚 𝑠𝑉=337.5 𝑚 𝑠𝑉= 𝑑 𝑡𝑡𝑉= 𝑑 𝑡 𝑡𝑑=𝑡𝑉𝑑=10.0𝑠(337.5 𝑚 𝑠 )𝒅=𝟑,𝟑𝟕𝟓.𝟎𝒎
5 Section 2: Properties of Sound Intensity and LoudnessThe amount of energy carried by a wave corresponds to the wave’s amplitudeIn a compressional wave, amplitude is related to the density of the particles in the compressions and rarefactionsLow energy = low densityHigh energy = high densityIntensity – the amount of energy that flows through a certain area in a specific amount of timeIntensity influences how far away a sound can be heardIntensity influences how far a wave will travel because some of the wave’s energy is converted to other forms of energy when it is passed from particle to particleLoudness is the human perception of sound intensityThe scale for measuring intensity (or loudness) of a sound is the decibel scalePitch and FrequencyPitch – how high or low a sound seems to bePitch and wave frequency are relatedThe higher the frequency of a sound wave, the higher the pitchThe human hearing range: 20-Hz to 20,000-HzUltrasonic waves –waves with frequencies greater than 20,000HzInfrasonic waves –waves with frequencies less than 20-Hz
6 Section 2: Properties of Sound The Doppler EffectDoppler Effect – the change in pitch or frequency due to a moving sound source or a moving observer Example: a police car siren:The siren from a stationary police car will sound the same regardless of where you are in relation to the car.When the car is in motion, a person standing in front on the car will hear the siren at a frequency higher than it actually is while a person behind the car will hear the siren at a frequency lower than it actually is.This occurs because the sound waves are compressed in front of the car (higher frequency) , and stretched behind the car (lower frequency)That same compression and stretching occur if an observer is moving in relation to a stationary source: moving towards the source seems to compress the sound waves while moving away from the source seems to stretch the sound waves.
7 Section 2: Properties of Sound The Doppler Effect (continued)There are four (4) equations used to describe the Doppler Effect:Source moving toward observer:Source moving away from observer:Observer moving toward source:Observer moving away from source:Two questions must be asked and answered before you can solve a Doppler Effect problem. The questions:What is moving, the sound source or the observer? If the source is moving use Eqs. 1 or 2. If the observer is moving use Eqs. 3 or 4.What is the direction of motion, toward or away from the observer or source? If the direction of motion is toward the observer or source use Eqs. 1 or 3. If the direction is away from observer or source use Eqs. 2 or 4Where:fo = frequency observer hearsfs = frequency of sound sourceV = speed of soundVs = speed of sourceVo = speed of observer
8 Section 2: Properties of Sound Example: Beth is standing on the corner of Main and Jackson when she hears the sound of an ambulance approaching her at 35 m/s. The temperature is 25oC, and ambulance siren sounds a steady 900 HZ. At what frequency does Beth hear the siren?SolutionSolution Steps:List the variables you know and the variable you are solving forSolve the equation for the speed of sound at that temperature (V)Ask and answer the two questions (What is moving? Direction of motion?) to determine which Doppler Effect equation to use. In the example, the source is moving toward the observer (use Equation 1)Solve the problem showing all work and dimensional analysis.Vs = 35.0m/sT = 25oCfs = Hzfo = ?