The Physics
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Frequency of Bat Sonar

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Bibliographic Entry Result
(w/surrounding text)
Ramsey, William L. Holt Physical Science. New York: Holt, 1986: 157. "10,000 Hz to 120,000 Hz" 10–120 kHz
"Sound." World Book Encyclopedia. Chicago: World Book, 1998: 600. "10,000 Hz to 120,000 Hz" 10–120 kHz
Wilson, Don E. Bats in Question: the Smithsonian Answer Book. Washington, DC: Smithsonian Institution Press, 1997: 15. "Beyond our hearing capacity anything over about 15 kHz" > 15 kHz
Giancoli, Douglas C. Physics: Principles with Applications. New Jersey: Prentice Hall, 1980: 309. "Bats can detect frequencies as high as 100,000 Hz" < 100 kHz
Davis, Wayne H. "Bat." Collier's Encyclopedia. New York: Macmillan, 1992: 698. "Echolocation sounds commonly range in frequency from 40,000 Hz to 100,000 Hz" 40–100 kHz

We as humans can hear many things. From the giant truck driving by to the writing of a pen. The few sounds we cannot hear are bat sounds. Their frequencies of producing sound is much higher than ours and so we can't hear it.

Frequency is how fast an object vibrates and sound vibrates in waves. The vibrations are measured in Hertz. So one Hertz (1 Hz) is equivalent to one vibration in a second. Humans can hear from 20 Hz to 20 kHz. Anything higher is called ultrasound or ultrasonic sound. The reason that bats use ultrasound is because it has such a high frequency and it has a low diffraction or it bends less. They use this sound to do a couple of things like to catch their prey and also just to get around. The method of doing such tasks is called echolocation. They make a sound and wait for it to bounce back to hear it. If they hear it come faster in a particular area than the rest of the sounds then they know that something is near. The frequencies of bats are different in many books found. In one source like the encyclopedia it says that the frequency is 120 kHz. While in another it says 100 kHz. The truth is it ranges because when the bat makes a sound it isn't of the same frequency all the time.

So, then the values the frequency ranges from are stated to be as low as 10 kHz to as high as 120 kHz.

Juan Cancel -- 1998

Bibliographic Entry Result
(w/surrounding text)
Cutnell, J.D. & Johnson, K.W. Physics. 3rd ed. New York: Wiley, 1995: 491. "up to a frequency of 100 kHz. < 100 kHz
MacDonald, D. "Bats." The Encyclopedia of Mammals. New York, 1984: 792-794. "Humans can perceive sounds from 20 Hz to 20,000 Hz while bats' sensitivity ranges from less than 100 Hz to 200,000 Hz (normally written as 200 kHz)." 0.1–200 kHz
Whitaker, J.O. National Audubon Society Field Guide to North American Mammals. New York, 1996: 312. "While flying the bat emits through its' mouth or nose a continuous series of supersonic [sic] sounds (some 30-60 squeaks per second) ranging in frequency or pitch from below 20 kHz up to about 100 kHz." 20–100 kHz
Long, M.R. & Savage, J.G. Mammal Evolution. New York: Harper, 1976: 108. "Most bats use frequencies in the range 20-80 kHz, only a few bats use frequencies less than 20 kHz which is the upper limit of human hearing." 20–80 kHz
[lost in cyberspace -- ed.]
"The actual cry is very short (1 ms), but consist of a sweep over 50 kHz." > 50 kHz

Bats are in the family Mammalia and in the order Chiroptera [literally, hand-wing]. They are night-flying mammals with forelimbs modified into wings. Ages before scientists developed sonar, bats were using sound waves for communication and navigation. At one time, people had thought that only bats possessed this ability, but later investigations have shown that a number of animals also use such means including some fish. Insect-eating bats are one of the animals with the best sonar.

In 1793, Lazzaro Spallanzani of Italy discovered that bats were not affected if their eyes were blindfolded but were disoriented if they could not hear. It was suggested by an English physiologist in 1920 that bats navigate, locate, and captured their prey by hearing. With the invention of the microphones sensitive to high frequencies in the 1930s, Donald Griffin discovered that bats produce ultrasonic sounds (sounds of higher frequency than those audible to humans). He taped one or both of their ears shut and found that the bats could no longer navigate. Experiments conducted with hundreds of wires crisscrossing an enclosure were used to demonstrate the sonic guidance of bats. It is now known that bats emit ultrasonic sounds ranging from 20 to 100 kHz. The sounds are emitted through the bats' mouth or nostrils and are aided by a complex flap-structure to provide directivity. The echo that returns from such emissions enable the bats to pick out tiny flying insects from some distance. The bats can also determine the size, location, density and movement of an object.

Audrey Chan -- 1998

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