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Unit 11 Speed of Sound Sound can travel through any kind of matter, but not through a . The speed of sound is different in different materials; in general, it is slowest in gases, faster in , and fastest in solids. The speed depends somewhat on , especially for gases.

vair = 331.0 + 0.60T T is the temperature in degrees Example 1:

Find the speed of a sound wave in air at a temperature of 20 degrees Celsius. v = 331 + (0.60) (20) v = 331 m/s + 12.0 m/s v = 343 m/s Using Wave Speed to Determine Distances At normal atmospheric and a temperature of 20 degrees Celsius, speed of sound: v = 343m / s = 3.43102 m / s Speed of sound 750 mi/h

Speed of light 670 616 629 mi/h

c = 300,000,000m / s = 3.00 108 m / s Delay between the thunder and Example 2:

The thunder is heard 3 seconds after the lightning seen. Find the distance to storm location. The speed of sound is 345 m/s. distance = v t = (345m/s)(3s) = 1035m Example 3:

Another phenomenon related to the perception of time delays between two events is an echo. In a canyon, an echo is heard 1.40 seconds after making the holler. Find the distance to the canyon wall (v=345m/s) distanceround trip = vt = (345 m/s )( 1.40 s) = 483 m d= 484/2=242m Applications: , Ultrasound, and Medical Imaging

• Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. • The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. Sonar (originally an acronym for SOund Navigati on And Ranging) 12-9 Applications: Sonar, Ultrasound, and Medical Imaging Sonar is used to locate objects underwater by measuring the time it takes a sound pulse to reflect back to the receiver. Similar techniques can be used to learn about the internal structure of the . Sonar usually uses ultrasound waves, as the shorter wavelengths are less likely to be diffracted by obstacles. 12-9 Applications: Sonar, Ultrasound, and Medical Imaging

Ultrasound is also used for medical imaging. Repeated traces are made as the transducer is moved, and a complete picture is built. Applications: Sonar, Ultrasound, and Medical Imaging 1. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. 2. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). 3. Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. 4. The reflected waves are picked up by the probe and relayed to the machine. 5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). 6. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below. Do Now

An oceanic depth-sounding vessel surveys the bottom with ultrasonic sound that travels 1530 m/s in seawater. Find the depth of the if the time delay of the echo to the ocean floor and back is 8 seconds.

dRoundTrip = vt = (1530 m/s)(8s) = 12240 m d= 12240 m/2=6120m Practice Problem 2: An automatic focus camera is able to focus on objects by use of an ultrasonic sound wave. The camera sends out sound waves that reflect off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If a sound wave (speed = 345 m/s) returns to the camera 0.115 seconds after leaving the camera, how far away is the object? droundtrip = vt = (345 m/s) (0.115s) = 39.7m d=39.7m/2=19.8m Practice Problem 3:

Miles Tugo is camping in Glacier National Park. In the midst of a glacier canyon, he makes a loud holler. The sound (v= 345m/s) bounces off the nearest canyon wall (which is located 170 m away from Miles) and returns to miles. Determine the time elapsed between when Mikes makes the holler and the echo heard. droundtrip= 2(170m)=340m t=droundtrip/v=340m/345m/s=0.985s Practice Problem 4:

Suppose that sound travels at a speed of 345 m/s on the evening of a . There is a lightning strike some distance from your home. The light reaches you nearly immediately. Yet the thunder is heard 3.5 seconds later. How many miles from your home did the lightning strike? (1609m=1mile)

d = vt = (345m / s)(3.5s) = 1207.5m

1207.5m 1mi  = 0.750mi 1 1609m