In this website, SI units have been used throughout. However, prior to this, metric units were in use, not only in India, but also in several parts of the world. Most of the equipment in these laboratories have the use of metric units. These equipment use grams and kilograms. Hence, mass units of grams and kilograms (formerly called ‘weight’) will continue to be used. Also, the term ‘mass’ and ‘weight’ are commonly used interchangeably. This may cause some problem with ‘unit weight’ terms. In this text, ‘mass’ will be represented in terms of grams and kilograms while ‘weight’ will be represented in terms of Newtons and kilo Newtons. The term density is defined as mass per unit volume; hence it will be represented in terms of g/cm3 or kg/m3 units. On the contrary, the term ‘unit weight’ is the weight per unit volume. Hence, it will be represented in terms of kN/m3.
The value of gravitational constant g will be taken as 981 cm/s2 (9.81 m/s2), for computational purposes.
Thus, in order to convert the density (expressed in terms of g/cm3) into unit weight, multiply the former by 9.81. For example, if a soil mass has a mass of 216 g and volume of 120 cm3.
- Density = (Mass/Vol.) = 216/120 = 1.8 g/cm3
- Unit Weight = (Weight/Vol.) = (216/120) x 9.81 = 17.66 kN/m3
Pressure, which is defined to be a force per unit area, will be expressed in terms of kN/m2 or in term of kilopascals (kPa).