Waves the transfer of energy without the transfer of matter

A Simple Look at a Wave crest trough wavelength amplitude λ λ A A How many wavelengths in the wave below?

frequency = how many λ pass per second units: per second units: per second

period= time for 1 λ to pass by or

Ex.The wave below takes 10 seconds to pass by. What is the period? What is the frequency?

Speed How fast a wave moves

Types of Waves Transverse wave: medium vibrates at right angles to the direction the energy moves Compression wave: (longitudinal wave) Compression wave: (longitudinal wave) medium vibrates in the same direction as the direction the energy moves λ λ

Types of Waves

Electromagnetic Waves Mechanical waves require a medium in order to travel. examples: electromagnetic waves do not require a medium water,earthquakes, and sound

Electromagnetic Waves All EM waves travel at 3.0 x 10 8 m/s

Electromagnetic Waves Radio waves are the longest of the spectrum

Electromagnetic Waves Visible light is a tiny section

Electromagnetic Waves Visible light is between ultraviolet (UV) light and Infrared (IR) light v v v v

Interference FSuperposition: when two or more waves overlap FWaves do not affect each others identity FSuperposition: when two or more waves overlap FWaves do not affect each others identity

Interference: Wave Addition

Interference Fwaves add together Foverall amplitude is sum of individual wave amplitudes FInterference ExampleInterference Example Fwaves add together Foverall amplitude is sum of individual wave amplitudes FInterference ExampleInterference Example

Practice Each wave pulse moves 1 grid at a time

Practice Each wave pulse moves 1 grid at a time

Practice sketch where wave would be if alone

Practice FWaves above rest are positive Fbelow are negative

Practice FAdd ‘em up

Practice FAdd ‘em up

Practice FAdd ‘em up

Practice FAdd ‘em up

Practice FAdd ‘em up

Practice FMove another grid and repeat process (remember, if both same sign then they stack/add) Now try it yourself

SOUND FSound is a compressional wave FSpeed of sound depends on the medium Ffastest in solids (6000 m/s in steel) Fslower in liquids (1500 m/s in water) Fslowest in gases FSound is a compressional wave FSpeed of sound depends on the medium Ffastest in solids (6000 m/s in steel) Fslower in liquids (1500 m/s in water) Fslowest in gases

Speed of sound in Air speed of sound at 0 °C At average temperature: 20 °C If no temperature is given in a problem, assume 20° C (343 m/s)

Distance FIf you hear lightning 3.0 seconds after seeing it, how far away did it strike?

Characterizing Sound FSounds waves are characterized by their: Fspeed Fpitch Floudness Fquality FSounds waves are characterized by their: Fspeed Fpitch Floudness Fquality

Pitch FPitch depends on frequency FYoung healthy human ear has a range of 20 Hz to 20,000 Hz FHuman voice: 120 Hz to 1,100 Hz FBaby cry: 2,000 – 3,000 Hz FTest your rangeTest your range FPitch depends on frequency FYoung healthy human ear has a range of 20 Hz to 20,000 Hz FHuman voice: 120 Hz to 1,100 Hz FBaby cry: 2,000 – 3,000 Hz FTest your rangeTest your range

Octaves FThe octave is important in music FOctave is the doubling in ƒ FEar can hear a range of ≈ 10 octaves F20 Hz  40 Hz  80 Hz  FThe octave is important in music FOctave is the doubling in ƒ FEar can hear a range of ≈ 10 octaves F20 Hz  40 Hz  80 Hz  160 Hz  320 Hz  640 Hz  1280 Hz  2560 Hz  5120 Hz  10,240 Hz  20,480 Hz

Just Noticeable Difference (JND) FThe range that the ear can distinguish tones (pitches) Fat <1000 Hz, JND ≈ 1Hz Fthis means you can tell the difference between 500 Hz and 501 Hz Fat 2,000 Hz, JND ≈ 2 Hz Fat 4,000 Hz, JND ≈ 10 Hz FTest itTest it FThe range that the ear can distinguish tones (pitches) Fat <1000 Hz, JND ≈ 1Hz Fthis means you can tell the difference between 500 Hz and 501 Hz Fat 2,000 Hz, JND ≈ 2 Hz Fat 4,000 Hz, JND ≈ 10 Hz FTest itTest it

Loudness of Sound Fdepends on amplitude of a sound wave Fnew unit  decibel (db) Fdecibel is based on human hearing F0 decibels is the threshold of hearing F140 db is the sound of a jet on runway Fdepends on amplitude of a sound wave Fnew unit  decibel (db) Fdecibel is based on human hearing F0 decibels is the threshold of hearing F140 db is the sound of a jet on runway

Loudness of Sound Fdecibel scale is logarithmic FSo, 60 db  70 db means 10x louder F60 db  80 db means 100x louder F140 db is 100,000,000,000,000x louder than 0 db FTest your rangeTest your range Fdecibel scale is logarithmic FSo, 60 db  70 db means 10x louder F60 db  80 db means 100x louder F140 db is 100,000,000,000,000x louder than 0 db FTest your rangeTest your range

Decibel Details FSound Intensity Level (L) = db Fmeasures how loud you perceive sound FSound Intensity (I) = W/m 2 Fmeasures physical intensity of sound Fthreshold I = 1 x W/m 2 FSound Intensity Level (L) = db Fmeasures how loud you perceive sound FSound Intensity (I) = W/m 2 Fmeasures physical intensity of sound Fthreshold I = 1 x W/m 2

Decibel Details Fthreshold = 0 db = 1 x W/m 2 I 2 = heard sound I 1 = sound you compare to (usually 1 x W/m 2 )

Example FHow many decibels would sound have if it had an intensity of 1 x W/m 2 ? for normal problems, use 1 x W/m 2 for I 1 given:

Example FWhat is the sound Intensity of a girl yelling at 86 db? but this time, we want I 2

Power! units are Watts (W) Energy rate produced by a sound

Power! Power depends only on source, not distance this can be used to find I at different distances Start with two instances of the sound (2 P’s)

Power Example: What is the power of a jet engine when standing 5.0 m away from it? given: r = 5.0 m L = 140 db given: r = 5.0 m L = 140 db need I first

Frequency Sensitivity The ear is much more sensitive to some pitches than others. How much more sensitive are we to a crying baby (3,000 Hz) than to normal talking (1,000 Hz)?

Practice go to page 129

Doppler Effect Pig standing still OINK! λ in front is same as λ behind

Doppler Effect Pig running right OINK! λ in front is smaller λ than behind Who hears the higher pitch?

Doppler for Everyone!

Calculating Doppler Effect FDoppler Effect occurs if either source or listener is moving ƒ ’ = frequency the observer hears ƒ = actual frequency of source ν = speed of sound (remember T) ν o = speed of observer ν s = speed of source

Picking Signs Ex: On a day when the speed of sound is 350 m/s, a police car with a 2,000 Hz siren and a speed of 35 m/s is chasing a car moving at 50. m/s. What frequency does the driver of the car hear? what is the source? police car (it has the siren) what is the observer? chased car Given: moving away from source moving toward the observer

Picking Signs Given: So, Now to pick signs. This requires logic.

Picking Signs If observer travels away from source, pitch goes down. If observer travels toward source, pitch goes up. Numerator (observer) for pitch to go down, v o must be negative for pitch to go up, v o must be positive

Picking Signs If source travels away from observer, pitch goes down. If source travels toward observer, pitch goes up. Denominator (source) for pitch to go down, v s must be positive for pitch to go up, v s must be negative

Put it together observer moving away from source  (-) source moving towards observer  (-) car hears a lower pitch!

Do you get it? Ex: It’s 33°C and you’re moving at 45 m/s on a head-on collision course with another car moving at 35 m/s. You lean on your 1,800 Hz horn. What frequency does the other driver hear? Given: moving toward the source moving toward the observer

Do you get it? Given: Find the speed (T = 33°C)

Do you get it? Given: moving toward the source moving toward the observer Pitch goes up! Now let’s choose signs

Faster than the Speed of Sound Objects moving faster than sound make shock waves from the pushed air and sound. An observer would hear this as a crack! See the sounds waves

Faster than the Speed of Sound Which plane is moving faster? Mach 3.5 Mach 6

Breaking the speed of sound

Practice go to page 140