Page 12 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

1.3 Unit Conversions

Measurements that describe physical quantities may be expressed in a variety of different

units. As a result, one often has to convert a quantity from one unit to another. For

example, we would like to convert, say, 49 days into weeks. One approach is to multiply

the value by ratios of the equivalent units. The ratios are formed such that the old units
are cancelled, leaving the new units

The example of unit conversions are:

❑ 1 kg = 1000 g

❑ 1 m = 100 cm = 1000 mm
5
6
❑ 1 km = 1000 m = (100 000 cm @ 10 cm) = (1 000 000 mm @ 10 mm)
❑ 1 hour = 60 minutes = 3600 seconds
3
-3
3
❑ 1 m = 1000 litre, or 1 litre = 1 x 10 m
2
5
2
2
❑ 1 bar = 1 x 10 N/m = 1 x 10 kN/m

Multiple and sub-multiple of the basic units are formed by means of prefixes, and the
ones most commonly used are shown in the following table:

Table 1.3-1 Multiplying factors

Multiplying Factor Prefix Symbol

12
1 000 000 000 000 10 tera T
9
1 000 000 000 10 giga G
6
1 000 000 10 mega M
3
1 000 10 kilo k
2
100 10 hector h
1
10 10 deca da
-1
0.1 10 desi d
-2
0.01 10 centi c
-3
0.001 10 milli m
-6
0.000 001 10 micro 
-9
0.000 000 001 10 nano n
-12
0.000 000 000 001 10 pico p

3 | P a g e