Sound Interference 44 BR COPY ALL on to

Sound & Interference

4/4 BR: COPY ALL on to Guided Notes: Characteristics of “Sound” Review l Compressional / Longitudinal wave l Mechanical wave/Transverse l v = 330 m/s in air at 0°C and 340 m/s at 20°C l As tempmedium ↑, velocity ↑ l As densitymedium ↑ , velocity ↑ l v = f *λ l As frequency ↑, wavelength (λ) ↓ l Frequency and pitch are related l Amplitude and “loudness” (decibels) are related

Frequency & Resonance

Human Hearing Range l l l The teacher will make a range of sounds. Record whether you can hear each frequency below. 1) 100 Hz 2) 440 Hz 3) 2, 000 Hz 4) 12, 000 Hz 5) 15, 000 Hz

Human Hearing Range l Human range is about 20 -20, 000 Hz l Older people and teens who listen to their music too loud tend to lose the high and low parts of their ranges A flute’s range is 247 Hz (low B) to 2792 Hz (high F). l Ultrasonic: sounds greater than 20, 000 Hz l Infrasonic: sounds less than 20 Hz l

Frequency Human hearing ~ 20 – 20, 000 Hz l “ULTRAsound” = “higher than we can hear” (anything above 20, 000 Hz). l

Doppler Effect - Demo Time!!! l Doppler Effect: the apparent change in pitch (frequency) due to position l l Listen: http: //www. ionaphysics. org/lab/Doppler. Demo. htm Draw: http: //www. lon-capa. org/~mmp/applist/doppler/d. htm Sketch the sound waves as the source is… Standing still Moving at Mach 0. 7 Moving at Mach 1. 4 (Supersonic)

Doppler Effect - Demo Time!!! l Pitch: the frequency of the sound wave l l High frequency waves = ____ pitch Low frequency waves = _____ pitch Low Intensity: the loudness, or amplitude of the sound How does the pitch perceived by the listener change as the siren approaches and then passes the listener? l Does the actual pitch of the siren change as it passes by? l l No, the actual pitch does not change. Intensity and apparent high pitch increases as siren approaches. Intensity and apparent low pitch decreases as siren leaves.

Sonic Boom l Sonic Boom Occurs when the object creating a sound moves faster than the sound waves it creates l Compressions constructively interfere l Ted https: //www. youtube. com/watch? v=JO 4_VH M 69 o. I l The Sound: https: //www. youtube. com/watch? v=OEmi. TY t. W 5 cs l

Sonic Boom l A Sonic Boom Credit: Ensign John Gay, USS Constellation, US Navy

Resonance Natural frequency – the frequency at which an object wants to vibrate l Resonance – when properly timed small impulses add up to make a much larger amplitude l l Ex: wine glass, breaking a glass with a voice

Frequency – Disaster! l When structures resonate, results can be disastrous l l Tacoma Narrows bridge collapse – 1940 “Galloping Gertie” Video Clip (full-length) https: //www. youtube. com/watch? v=n. Fzu 6 CNtqe c

Doppler Effect

How Does Radar Work

B-2 Spirit Stealth Bomber. Photo by Bobbi Garcia. Posted here with permission of the AFFTC.

F/A 9 -Lives ……. super sonic kitty

Doppler Formula Observer speed Source speed Perceived frequency Actual frequency Wave speed + if approaching - if receding

No one move!

Observer moves + if approaching - if receding

Source moves + if approaching - if receding

Interference & Beats

Demo Time!!! l Hoot Tube l l One end is open Singing Rod l Both ends are open finger

Open at both ends: Open at only one end:

Beats – let’s listen! l Beats http: //library. thinkquest. org/19537/java/B eats. html l Ruben’s Board https: //www. youtube. com/watch? v=2 awb KQ 2 DLRE&t=324 s l Ruben’s Tube https: //www. youtube. com/watch? v=gp. Cq u. UWqa. Yw

Interference & Beats l Beats Created by constructive & destructive interference l Periods of loud sounds followed by soft sounds l Two waves of different frequencies interfere with each other l

Interference & Beats l Beat Frequency l Determined by the difference between the two frequencies l 300 Hz sound wave and 302 Hz sound wave will produce 2 beats per second – “Beat Frequency” is 2 Hz

Constants Based on your knowledge how sound travels in different media, rank the following from transmitting sound fastest to slowest: 2 3 1 ___Water ___Air ___Solid l Speed of sound at 0°C: 330 m/s l Speed of sound at 22°C: 343 m/s l l Example: Calculate the speed of sound in air at -15°C.