Name: Period Sound Unit 10:5 What is Sound? Sound Wave are Pressure Waves Sound is the movement of Sound source As a wave sound needs a low pressure human ear medium to travel compression waves through. Sound cannot (longitudinal waves) hitting .... . . .... travel through the vac- our ears. These compression uum of space. Spa silent (no matter what waves are alternating high you hear in the movies). and low pressure areas. The high air molecules vibrate back pressure and forth, but don't travel. On graphs, Tiny hairs inside the we use cochlea (inner ear) cochlea crest's and translate air pressure troughs to into electrical im- Speakers imitate show high pulses that can be sounds by pushing air and causing and low read by the brain. Very loud sounds vibrations. pressure. low pressure bend these hairs, causing deafness. Frequency = Pitch Higher Frequency = Higher Pitch Elephants and submarines use Frequency (f) Wavelength (2) Source infrasonic sound We hear the frequency of 20 Hz 17 m rumble of thunder (too low to hear) sound as pitch. A higher to communicate 100 Hz 3.4 m bass guitar over long distances. Very low frequency we hear 2,000 Hz 17 cm fire truck siren frequencies (very bass) travel very higher pitch. A lower long distances and can penetrate frequency we hear as 4,000 Hz 7 cm highest note of piano through water (just like thru cars) a lower pitch. 10,000 Hz 3.4 cm whine of a jet turbine Dog whistles use ultra- Humans can hear frequencies that are sonic frequencies (above human hearing [+20,000 Hz]), between 20 Hz and 20,000 Hz! but perfect for dog ears! Amplitude = Loudness Loudness is measured in decibels (dB) A +10 dB change we 10 dB Total silence. hear as twice as loud. We hear pressure (the 30 dB Total quiet in the woods at night. A 30 dB sound is twice as amplitude) of sound as loud as a 20 dB sound. 50 dB Normal conversation. loudness. It takes more energy to create a louder 70 dB Busy traffic in the city. A -10 dB change we sound. Too loud of a 90 dB A jackhammer (hearing damage if not protected) hear as half as loud. sound can cause deafness. 110 dB Threshold of pain from sound. A 30 dB sound is half as 200 dB Human will die from the sound pressure. loud as a 40 dB sound. Speed of Sound (Vs) The speed of sound in air is about 340 m/sec. You can use v; = f2. to find frequency or wavelength. The speed of sound changes. AND use S = D/T to find distance or time. In gases, hotter (faster) gases In both cases, Vs (S) is a constant for sound: 340 m/sec. conduct sound faster. In solids and liquids, generally denser Ex. Find the wavelength of a 200 H- sound. (tighter) materials are faster. Motion faster than sound is called Vs = 340 m's v = f). so ) = v/f supersonic. Supersonic planes give their speed in multiples of Mach Material Vs (m/sec) f = 200 Hz 2 = (340 m/s) = (200 Hz) (1 x the speed of sound). 340 2 = ? 2 1.7 m Air Mach 1 = 340 mi's. Helium 965 Ex. If you hear a sound 3 seconds after you Mach 2 = 680 m/s. Water 1530 see the motion. How far away is it? A sonic boom is caused by an object Wood 2000 Vs = 340 m/'s Vs = D/T so D = vs T breaking through the sound barrier. Gold 3240 T = 3 sec D = (340 m/s) X (3 sec) Supersonic planes, bullets, and Steel 5940 D = ? D - 1020 m bullwhips all make sonic booms. Copyright @ 2014, C. Stephen Murray ephenmurray.comName: Unit 10:5 Period: 1. Sound A. Faster than the speed of sound. 1. Pitch A. Where there is no sound because of its vacuum. 2. Sonic boom B. A wave caused by alternating high and 2. dB low pressure. B. How we hear changes of frequency of 3. Supersonic C. The organ that detects sound waves. 3. Space sound. 340 m's in air. 4. Ultrasonic D. A pressure wave caused by an object go- C. ing faster than sound. 4. Loudness D. How we measure loudness. 5. Cochlea E. A sound higher than humans can hear. 5. Vs E. The amplitude or strength of a sound. Displacement vs. Position Use the graph to answer these questions: = I cycle is from I'm to 1/2 cycle is from 0 m to Amplitude (A) = Total cycles: ENCO EQUILAID UAWNHO - NW AUT It is a sound wave: find frequency: Is this frequency audible to humans (can we hear it)? Position (m) A wave's velocity is 90 m/sec with a frequency of 6 Hz. What is Why is space silent? it's wavelength? If I increase the energy I give a sound wave what changes: A sound wave has a wavelength of 20 m. Find its frequency. If a wave's fourth harmonic has a frequency of 40 Hz. what is its natural frequency and what is the frequency of He? If a sound wave's frequency is 100 Hz. What is its period? What is the above wave's wavelength? If a wave's fundamental is 6 Hz, what harmonic has a frequency of 4S HZ? A railroad crew is repairing a rail. You hear the hammer 0.5 sec- onds after it is swung. How far away is the crew? Find its period: 80 HZ What harmonic is this? You hear a plane 4 seconds after you see it. Find the distance to Could a human hear this frequency? the plane. Mark the nodes and anti-nodes. How many wavelengths is it? What is its wavelength? 6 m If a sound is 40 dB loud. Answer how many dB these would be: Find the fundamental frequency: 1) A sound twice as loud: 2) A sound half as loud: 5th harmonic frequency: Compared to a 50 dB sound, you would hear a 60 dB as: Speed of the wave on this string: cstephenmurray.com Copyright @ 2014, C. Stephen Murray