Handbook for Sound Engineers

1650 Chapter 48

Force (F). Force is any action that changes, or tends to
change, a body’s state of rest or uniform motion in a
straight line.

The newton (N) is the unit of force and is that force
which, when applied to a body having a mass of 1 kg,
gives it an acceleration of 1 m/s^2. One newton equals
1 J/m, 1 kg(m)/s^2 , 10^5 dynes, and 0.224 809 lb force.

Pressure. Pressure is the force (in a fluid) exerted per
unit area on an infinitesimal plane situated at the point.
In a fluid at rest, the pressure at any point is the same in
all directions. A fluid is any material substance which in
static equilibrium cannot exert tangential force across a
surface but can exert only pressure. Liquids and gases
are fluids.

The pascal (Pa) is the unit of pressure. The pascal is
equal to the newton per square meter (N/m^2 ).

(48-7)

Power (W). Power is the rate at which energy is
expended or work is done. The watt (W) is the unit of
power and is the power that generates energy at the rate
of 1 J/s.

(48-8)

Electric Charge (Q). Electric charge is the quantity of
electricity or electrons that flows past a point in a period
of time. The coulomb (C) is the unit of electric charge
and is the quantity of electricity moved in 1 second by a
current of 1 ampere. The coulomb is also defined as
6.24196 × 10^18 electronic charges.

Electric Potential Difference (V). Often called elec-
tromotive force (emf) and voltage (V), electric potential
difference is the line integral of the electric field
strength between two points. The volt (V) is the unit of
electric potential. The volt is the potential difference
that will cause a current flow of 1 A between two points
in a circuit when the power dissipated between those
two points is 1 W.

A simpler definition would be to say a potential
difference of 1 V will drive a current of 1 A through a
resistance of 1:..

(48-9)

Electric Resistance (R). Electric resistance is the prop-

erty of conductors that, depending in their dimensions,

material, and temperature, determines the current

produced by a given difference of potential. It is also

that property of a substance that impedes current and

results in the dissipation of power in the form of heat.

The ohm (:) is the unit of resistance and is the resis-

tance that will limit the current flow to 1 A when a

potential difference of 1 V is applied to it.

(48-10)

Electric Conductance (G). Electric conductance is the

reciprocal of resistance. The siemens (S) is the unit of

electric conductance. A passive device that has a

conductance of 1 S will allow a current flow of 1 A

when 1 V potential is applied to it.

(48-11)

Electric Capacitance (C). Electric capacitance is the

property of an isolated conductor or set of conductors

and insulators to store electric charge. The farad (F) is

the unit of electric capacitance and is defined as the

capacitance that exhibits a potential difference of 1 V

when it holds a charge of 1 C.

(48-12)

where,

C is the electric charge in coulombs,

V is the electric potential difference in volts,

A is the current in amperes,

1 Pa= 10 6–bars

1.45038 10

4–

u lb/in

2

=

1W=1J/s

=3.141442 BTU/h

=44.2537 ft-lb/min

=0.00134102 hp

Volt V W

A

---- -=

J

As

-----------=

kg m 2

s^3 A

=------------------

=A:

R V

A

= ---

kg m

2

s

3

A

----------------- 3 -=

S^1

:

= ----

A

V

= ---

F C

V

--- -=

AS

V

------ -=