Physics LG Sound Sept. 14, 2007

Physics notes:

Sound

Sound - is caused by a vibration needs a medium to travel through

Bell Jar demo

2How is sound made? Sound is caused by a vibration. If you put your fingers to your throat and hum, you can feel the vibrations. If you have seen someone with a large stereo in their car, you may have seen the whole car vibrating. That is because the speakers move back and forth or vibrating which causes the air to vibrate, thats sound. Sound need something to travel through. It cannot travel through a vacuum like outer space. This is one way sound and light are different, light can travel through a vacuum. We usually talk about sound as it travels through air. Sound can travel through solids, liquids and gasses. If you have every been underwater and heard something, it sounds funny. That is because sound travels faster in water as compared to air. Bell Jar DemoWhen you hear sound, how do you describe it? Loud? Pitch? We are going to talk about two components to sound. Loudness which depends mostly on amplitude. Another way of saying loudness is volume, how loud it is. I say it depends mostly on amplitude because we perceive some frequencies louder than others of the same amplitude. The second component of sound Im going to talk about is pitch which is determined by frequency. Pitch is how we perceive frequency. How does it sound to our ear. Is it high pitch or low pitch? In general, girls voice are higher pitched than boys. Loudness- depends mostly on amplitude- determined by the amount of pressure produced by a wave - measured in decibels (dB)

3Loudness is determined by the amount of pressure produced by a wave. In transverse waves, it is easy to image the amplitude increasing, the crest just gets higher, but in longitudinal waves, to increase the amplitude, you increase the scrunched area.

Loudness is measured in decibels. Symbolized by a small d, capital B.

This chart shows the frequency vs loudness. The green lines represent equal loudness levels. If you follow the bottom line, you see that lower frequencies need to be played louder than high frequencies to get the same perception of loudness. I think you can image this, if there is a squeaking noise, like nails on a chalkboard, even if it is quiet, you hear it clearly. But in general if you turn up the volume, you are increasing the amplitude!

threshold of pain = 130dB.

80 dB = protect your ears!!

normal conversation = 60 dB.

softest audible sound = threshold of hearing = 10 dB.

4The softest sound you can hear, the softest audible sound is called the threshold of hearing and is about 10 dB. An example of this would be a whisper or trees rustling.

A normal conversation is about 60 dB.

Starting at 80 dB, you should protect your ears. Look at the words along side the chart. Quiet, normal, loud, danger, harmful. Most concerts are in the danger zone. I went to a Kenny Chesney concert once and couldnt hear properly for a day or so. My hearing came back, but not all of it. Some people think that because your hearing comes back, you are ok, but that is not true. Every time you go above 80 dB, you do permanent damage to your hearing.

We also have the threshold of pain which is 130 dB.

5This is just to get a feeling of how loud things are and what amount of decibels correspond to it. Pitch determined by frequencymeasured in Hz

Frequency doubles=pitch goes up an octave

Pitch:many animals can make sounds and hear frequencies that humans can not.Ultrasonic - above 20,000 Hzex. Ultrasound, bats, dog whistle

Infrasonic - below 20 Hzex. whales, some birds, rhinos

Audible sound - 20 Hz to 20,000 Hz ex. limits of human hearing

our ears are amazing! they can distinguish 300,000 different tones!listen of this!Have one member of your team collect some response cards.8Need pre and post 1983 pennies. We know what sound is, how it is made and how it travels. But how do we hear it? How does our sense of hearing work?

SMARTnotebookNow we know what sound is, but how does a sound wave get to your ear?

An area of high pressure is called a compression.

An area of low pressure is called a rarefaction.As the tuning fork tines vibrate, it disturbs the air.

11But how does a sound wave get to your ear?

As the tuning fork tines vibrate, it disturbs the air around the tine.

As the tine moves outward, it forces the air molecules near it closer together. This produces a high pressure area called a compression.

As the tine moves inward, the air molecules spread out. This produces an area of low pressure called a rarefaction.

compression rarefactiona wave of compressions (squishes) and rarefactions (stretches) is called a longitudinal wave. we will be doing a lab on the speed of sound in the air using tuning forks.http://www.sengpielaudio.com/calculator-speedsound.htm

the doppler effect = change in frequency due to motion

14car horn as it passes

Doppler Demoshttp://www.walter-fendt.de/ph11e/dopplereff.htm

doppler rocket demo

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doppler effect

doppler effect contd

doppler effect still contd

Mach 1sonic boomExplosive sound caused by the shock wave of an aircraft traveling at super sonic speedsSuper sonic speeds means traveling faster than its own sound Series of pressure waves in front of and behind the aircraftCreates an enormous amount of sound energy released as a boom even with a volcanohttp://www.dailymail.co.uk/sciencetech/article-2747577/Holy-smokes-Watch-explosive-moment-volcano-erupts-triggers-SONIC-BOOM-sending-shockwaves-sky.html doppler effect phenomena summary give a signaled responseReceived Frequency Compared to Source FrequencyWavelength Compared to RestSpeed Relative to ObserverSource moves toward observerGreaterSmallerSameSource moves away from observerSmallerLargerSameSource and observer at restSameSameSame

Speed of SoundIt is storming outside, do you hear the thunder before or after seeing the lightning bolt?Sound < Light

The answer lies within the medium the sound travels in.

- dry air at 0C = 330 m / s = 1200 km/hr = 1/1,000,000 the speed of lightSpeed of SoundHow fast does sound travel?Trick question!

factors that affect the speed of sound...What does sound travel through the fastest; gas, liquid, solid?Fastest through a solidSlowest through a gasGas < Liquid < Solid

factors affecting sound contdwater vapor increases speed slightlyincrease temperature = increased speed (slightly)Think for a second, why would this be true?Faster moving molecules in warm air bump into each other more often therefore transmit the pulse in less time

bending of sound waves when air is cooler near ground.http://www.telegraph.co.uk/technology/news/10235261/Inside-the-Hyperloop-the-pneumatic-travel-system-faster-than-the-speed-of-sound.html https://www.youtube.com/watch?v=40pRYAAxf-s