A pressure variation that is transmitted through matter Chapter 15 – SOUND A pressure variation that is transmitted through matter They are mechanical Longitudinal waves Transmit energy

Problems will give you speed or if not use reference table Speed of sound waves depends on - Sound wave speed in air is _______331m/s - 0°C or STP and 343 m/s – 20°C__ room temp Problems will give you speed or if not use reference table Formula for speed of sound is v = λf Speed of sound is ___ vsolids > vliquids > vgases in solids and liquids than in gases. BUT IT ALSO DEPENDS ON ELASTICITY AND DENSITY Faster in warm air than in cold Sound ___doesn’t___________________ travel in a vacuum because _____there are no particles to interact

Sound waves – reflect off hard objects - reflected sound waves are called ____echoes_______________ Using the time required for an echo to return to a source can be used to find distance between source and reflective object. Remember that to hear the echo it has to travel there and back so take half of the time. Example: Ellie Yodeler gave a shout out across a valley to a cliff . It took 1 second for her echo to come back. How far away was the cliff? If no other info is given, use the speed of sound from your reference table. 3.31 X 10 ^2 m/s So what time do we use? .5 seconds to get there as it had to get there then back for us to hear. v = λf = d/t v = 3.31 X 10 ^2 m/s = d/ .5 sec V = 165.5 meters

Can diffract – bend as they go through openings Diffraction - waves squeeze through openings Have dead spots caused by interference of two waves

Can diffract – bend as they go through openings Have dead spots caused by interference of two waves - diffraction

Speed of a sound wave is calculated by: v = λf Ex: A tuning fork produces a sound wave in air with frequency of 261.6 Hz. At room temperature, the speed of sound is 343 m/s. What is the wavelength? V = λf 343 m/s = λ X 261.6 Hz λ = 343 m/s = Answer on next slide 261.6 Hz

1.311 meters

how far away is the sound if sound is travelling at 343 m/s? If you clap your hands and hear the echo from a distant wall.20 s later, how far away is the sound if sound is travelling at 343 m/s? V = 343 m/s t = .10 seconds ( remember there and back) V = d/t 343 m/s = d/.10 sec D = ANSWER ON NEXT SLIDE

34.3 meters

Find the frequency of a sound wave moving at 343m/s with a wavelength of .667 m. Answer on next slide

514.24 Hz

What is the frequency of sound in air at 20 degrees C having a wavelength equal to the diameter of a 38cm woofer loudspeaker? Of a 7.6 cm tweeter? Use the speed of sound at 343 m/s Answers on next slide

902.63 HZ and 4513 Hz

Doppler and Resonance Doppler Shift - occurs in all wave motion, mechanical and electromagnetic Has to do with our ears perception of the sound A sound gets closer the frequency that reaches our ears is greater due to decreasing distance so high pitch As sound goes away, the frequency that reaches our ears is less due to increasing distance Why does a siren sound high as it nears you and low as it goes away from you?

Resonance When air in a column vibrates at the same frequency it is in resonance. Resonance increases amplitude of a vibration/ Resonance effects are characterized by vibrations with large amplitude Why would it? http://www.youtube.com/watch?v=j-zczJXSxnw&feature=player_detailpage http://www.youtube.com/watch?feature=player_embedded&v=X5Uy7MhFiWA

A tuning fork can cause resonance in a tube with one end in water. A tube where one end is closed it is a closed end resonator. The length of the air column can be changed by lifting the tube in and out of the water until the sound gets louder as it becomes in resonance with the tuning fork. In closed pipes, resonant lengths are usually spaced ½ wavelengths apart. So if the difference is ½ λ 2 times the difference = λ Sometimes they are ¼ of a wavelength apart. We will use ½ wavelength.

When a tuning fork with a frequency of 392 Hz is used with a closed pipe resonator, the loudest sound Is heard when the column is at 21 cm and 65.3 cm. The air temp is 27° c. What is the speed of sound at this temp? Λ = 2 x difference of .653 - .21 m A 440 Hz tuning fork is held above a closed pipe. Find the spacings between the resonances when the air temp is 20 degrees C. Use 343m/s The 440 Hz tuning fork is used with a column to determine the velocity of helium. If the spacings are 110 cm, what is the velocity of sound in Helium?