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 12 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

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