PRE-PUBLICA TION EDITION - Nelson Education

5Using Mathematics in ScienceEffective communication of experimental data is animportant part of science. To avoid confusion whenreporting measurements or using measurements incalculations, there are a few accepted conventionsand practices that should be followed.5.A. SI UnitsThe scientific communities of many countries,including Canada, have agreed on a system ofmeasurement called SI (Système internationald’unités). This system consists of the sevenfundamental SI units, called base units, shownin Table 1.Table 1 The Seven SI Base UnitsQuantity name Unit name Unit symbollength metre mmass kilogram kg*time second selectric current ampere Atemperature kelvin K**amount of substance mole mollight intensity candela cd*The kilogram is the only base unit that contains a prefix.**Although the base unit for temperature is a kelvin (K), the common unit fortemperature is a degree Celsius (°C).All other physical quantities can be expressedas a combination of these seven SI base units. Forexample, the speed of an object is determined bythe distance it travels in a specified time period.Therefore, the unit for speed is metres (distance) persecond (time) or m/s. Units that are formed usingtwo or more base units are called derived units. Somederived units have special names and symbols. Forexample, the unit of force that causes a mass of 1 kgto accelerate at a rate of 1 m/s 2 (metre per second persecond) is known as a newton (N). In base units, thenewton is m·kg/s 2 . The dot between m and kg means“multiplied by,” but m·kg is simply read as “metrekilogram.” The slash means “divided by” and is read“per.” The whole unit is read “metre kilogram persecond squared.” You can see why a special nameand symbol are given to some derived units.Some common quantities and their units are listedin Table 2. Note that the symbols representing thequantities are italicized, whereas the unit symbolsare not.Table 2 Common Quantities and UnitsQuantity nameQuantitysymbolUnit nameUnitsymboldistance d metre marea A square metre m 2volumeVcubic metre m 3litrespeed v metre per second m/sacceleration a metre per secondper second5.A.1 Converting UnitsAn important feature of SI is the use of prefixesto express small or large sizes of any quantityconveniently. SI prefixes act as multipliers to increaseor decrease the value of a number in multiples of10 (Table 3). The most common prefixes change thesize in multiples of 1000 (10 3 or 10 −3 ), except forcenti (10 −2 ), as in centimetre.Lm/s 2concentration c gram per litre g/Ltemperature t degree Celsius °Cpressure p pascal Paenergy E joule Jwork W joule Jpower P watt Welectric potential V volt VelectricalresistanceR ohm Ωcurrent I ampere A624 Skills Handbook NEL