Fundamentals Chapter 1 1 1.1 Units Wherever measurements are performed there is a need for a coherent and practical system of units. In science and engineering the International System of units (SI units) form the basis of all units used. There are seven ‘ base ’ units from which all the other units are derived, called derived units. Table 1.1 The SI base units QuantityUnitUnit symbol MasskilogramkgLengthmetre mTime seconds Electric current ampere ATemperature kelvinK Luminous intensity candelacd Amount of substance molemol A few examples of derived units are shown in Table 1.2 , and it is worth noting that different symbols are used to represent the quantity and its associated unit in each case. For a more comprehensive list of SI units see Appendix A at the back of the book. Table 1.2 Some SI derived units Quantity Unit NameSymbolNameSymbolForce FNewtonNPowerPWatt WEnergyWJouleJResistanceROhm