Friday, December 6, 2013

Koala Vocal Cords

Recently, Benjamin Charlton and his colleagues discovered a new set of vocal cords in male koalas that allows them to produce mating calls at extremely low frequencies. By dissecting 10 koalas, the authors found another pair of cords previously unknown to scientists, which they dubbed "velar vocal cords." 

These calls, which sound like snorts and growls, have been recorded at frequencies in the range usually reserved for elephants, or 27.1 Hz. In order to put into perspective how incredibly low this is, I decided to calculate the speed of the vocal cords and compare that to the speed of the average male vocal cords. I also calculated how much Force is needed to make the vocal cords vibrate at this speed. 

To find the speed:
frequency= 27.1 Hz    length of vocal cords= 32.8 mm   so r= 0.019 m                                 
27.1 Hz * 2π = 170.3 rad/s = ω
v=ωr        v=(170.3 rad/s)(0.019)     v=3.24 m/s
3.24 m/s (1 mile/1609.3 m)(60 s/1 min)(60 min/1 hr) = 7.25 mph

Male Humans:
frequency= 125 Hz     length of vocal cords= 20 mm    so r=0.01 m
125 Hz * 2π = 785.4 rad/s = ω
v=ωr        v=(785.4 rad/s)(0.01)     v=7.85 m/s
7.85 m/s (1 mile/1609.3 m)(60 s/1 min)(60 min/1 hr) = 17.6 mph

To find the Force needed:
To make a 30 second call
vf=v0 + at
3.24 m/s = 0 m/s + a (30 sec)
a= .108 m/s2

F=(.00546 kg)(.108 m/s2)
F= 5.90 x 10^-4

So the speed at which the vocal cords vibrate is less than half that of the average male's speed, no wonder all of the lady koala's go wild for this call!


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