ELEMENTS 51 



Equation 4.4 states that the driving force or electromotive force across 

 an inductance is proportional to the inductance and the rate of change of 

 current. 



B. Inertia. — Mass is the mechanical element which opposes a change 

 in velocity. Mass is defined as 



/„ = »- 4.5 



where m — mass in grams, 



■ — ■ = acceleration, in centimeters per second per second, and 

 dt 



Jm = driving force, in dynes. 



Equation 4.5 states that the driving force applied to the mass is pro- 

 portional to the mass and the rate of change of velocity. 



C. Inertance. — Inertance is the acoustical element which opposes a 

 change in volume current. Inertance is defined as 



dU 

 p = M -— 4.6 



^ dt 



where M = inertance, in grams per square centimeter per square centi- 

 meter, 



^^ u • 1 • u- • 



— = change m volume current, m cubic centimeters per second 



dt 



per second, and 

 p = driving pressure, in dynes per square centimeter. 



Equation 4.6 states that the driving pressure applied to an inertance is 

 proportional to the inertance and the rate of change of volume current. 



4.4. Capacitance, Compliance, Acoustic Capacitance. — A. Electrical 

 Capacitance. — Capacitance is the electrical circuit element which opposes 

 a change in voltage. Capacitance is defined as 



i = Ce— 4.7 



where Ce = capacitance, in abfarads, 



de 



— = rate of change in voltage, in abvolts per second, and 



dt 



i = current, in abamperes. 



