60
2.4.1 Density and Its Importance
Density is the mass of substance per unit volume. It varies with temperature.
Mathematically, density is defined as:
ρ = m V
/
Where
ρ = density
m = mass
V = volume
The density of any fluid depends on components in it such as contaminants in
polluted water. Blood is composed of roughly 55% fluid plasma as well as 45%
cells. Blood density (Table  2.5) also varies among species and genders within a
species.
2.4.2 Pressure of Fluid at Rest
If a point in the fluid is assumed of as an infinitesimally small cube, then from the
principles of equilibrium the pressure on every side of this unit of fluid will be equal.
Pressure on a body submerged in a fluid is:
P
gh
= ρ
Where
ρ = density of the fluid
g = acceleration due to gravity
h = height of the fluid above the object
If the container is open to the atmosphere above, then:
P
P
P
total
a tmosphere
fluid
=
+
Table 2.5 Density of blood and its components
Bibliographic entry
Substance
Density (kg/
m
3
)
Cutnell and Johnson (1998)
Human blood
1060
Funk and Wagnalls (1985)
Human blood
1056–1066
Hinghofer-Szalkay and
Greenleaf (1987)
Human blood
1043–1057
Ageyama et al. (2001)
Blood of cynomolgus monkeys, squirrel
monkeys, and tamarins
1052.2–
1058.1
2 Fundamentals of Physics for Environmental and Medical Professionals