Modeling Speech and Hearing
Activity SH5.0v2
Activity 5: Homework
1. What should happen to the air speed as the air travels from the trachea through the glottis
during phonation?
2a. Assume that the trachea can be modeled as a cylindrical tube. A typical radius of the trachea
for a human male is 8.0 [mm]. If the air moves at 1.8 [m/s] in the trachea of this person then
what is the volume flow rate of the air?
b. If the vocal folds are partially open so that the cross-sectional area is about ¼ that of the
trachea then what is the volume flow rate in the glottis (the opening between the vocal folds)?
Assume that the air is incompressible.
c. What is the air speed in the glottis?
d. How will the air pressure in the glottis compare with the pressure in the trachea at this
moment?
Answers:
1. The equation of continuity suggests that air speed should go up since cross-sectional area goes
down.
2a. FV  Av    0.0080 1.8  3.6 104 m3 / s 
2
b. If the equation of continuity is correct then the flow rate is the same as in the trachea. So, FV =
3.6x10-4 [m3/s].
FV 3.6 104
m

 7.2  
c. v 
4
A 2.0 10
s
4
d. Bernoulli’s equation suggests that the pressure is lower in the glottis.
Activity Guide
 2007 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and DUE #00-88780