Date post: | 08-Aug-2015 |
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Science |
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Why can dogs hear things humans cannot?
SOUND WAVES
A SOUND WAVE IS A LONGITUDINAL PRESSURE WAVE CONSISTING OF
COMPRESSIONS AND RAREFRACTIONS
Frequency of a longitudinal wave refers to number of cycle (wavelengths) per second
Humans can generally hear 20-20 000 HzDogs can generally hear 40-60 000 HzThat means dogs can hear approximately 40 000
frequencies that are inaudible to us
THE FREQUENCY OF SOUND IS MEASURED IN HERTZ (HZ)
Pitch refers to frequency. A higher frequency produces a high pitch
Loudness depends on amplitude. A greater amplitude produces a louder sound
Wave speed depends on the medium through which the wave is transmitted. Sound travels faster in a solid than a liquid, and a liquid than a gas.
The bulk modulus (B) refers to the amount which a volume is changed by a pressureΔ
The speed of sound can also be given with respect to B
SOME IMPORTANT TERMS RELATING TO SOUND WAVES
v=λ fB= -V*ΔP ΔV
v=√(B/ρ)
Q) Amanda blows a whistle in her backyard. The package for the whistle gave the wavelength as 16 cm, and it also gave the frequency but it was scratched off. Knowing that the bulk modulus for air (at 20 C) is 1.01x105 Pa, and the density of air is 1.2 kg/m3,
A) What is the frequency of the whistle?B) Will Amanda hear it?C) Will Amanda’s dog, who is sitting at her feet, hear
it?D) Would a bat hear it? (Bats hear a frequency of app.
15-90 kHz)Try it now before looking at the walkthrough on the next slides!
TEST YOUR KNOWLEDGE
Using our equation v=√(B/ρ) combined with v=λ f we can use substitution to create an equation for frequency that uses only the information we have:
v=λ f f=v/λ where v=√(B/ρ) therefor f=(√(B/ρ) )/λNow we can sub in our values:*Remember to convert centimeters to meters for your
wavelength f=(√(1.01x105 Pa/1.2 kg/m3) )/0.012m=24 176.2 Hz 24.2 kHz
A) WHAT IS THE FREQUENCY OF THE WHISTLE
No, 24.2 kHz is outside of the average humans hearing capacity of 20-20 000 Hz.
B) CAN AMANDA HEAR IT?
I can’t hear anything!
Probably, 24.2 Hz is well within the average canine hearing capacity of 40-60 000 Hz
C) WILL AMANDA’S DOG, WHO IS SITTING AT HER FEET, HEAR IT?
Yes, it is also within the range of the bats hearing capacity
D) WOULD A BAT HEAR IT?
Image and information sources: http://revisionworld.com/gcse-revision/physics/waves/
describing-waveshttp://en.wikipedia.org/wiki/Hearing_range#Batshttp://www.privateline.com/TelephoneHistory/
soundwaves.html
THANKS FOR WATCHING