Units
TABLE 1.2. Accepted SI prefixed and symbols for multiples
and submultiples of units.
Multiplication Factor
Prefix
Symbol
exa
Pets
tera
gigs
mega
kilo
hecto
deka
deci
centi
milli
micro
nano
pic0
femto
atto
Solution. Table A.4 gives the conversion, 1 J = 0.2388 cal so
3.9kcal
103cal
103g
X - X -
1 J
J
x
= 16.3 x lo6 -
g
kcal
kg
0.2388 cal
kg
= 16.3 MJ/kg.
Example 1.2. Chapter 2 gives a formula for computing the damping
depth of temperature fluctuations in soil as D = k , where K is the
Lthermal diffusivity of the soil and w is the angular frequency of temperature fluctuations at the surface. Figure 8.4 shows that a typical diffusivity for soil is around 0.4mm
2
/s. Find the diurnal damping depth.
Solution. The angular frequency is 2n/P, where P is the period of
temperature fluctuations. For diurnal variations, the period is one day
(see Chs. 2 & 8 for more details) so w = 2 n l l day. Converting w and K
to SI base units gives:
2n
1 day
1 hr
1 min
w=x - x - X - = 7.3 x 1 0 - ~ s-'
1 day
24hr
60min
60 s