IB Physics C.D.Cameron International School of Geneva

SI Units Fundamental Units: those which can't be expressed in terms of others (there are exceptions). Mass, length, time, electric current. Fundamental Units: those which can't be expressed in terms of others (there are exceptions). Mass, length, time, electric current. QuantityUnit Symbol QuantityUnit Symbol Masskilogramkg Masskilogramkg Lengthmeterm Lengthmeterm Timeseconds Timeseconds Electric currentampereA Electric currentampereA TemperaturekelvinK TemperaturekelvinK Amount of substancemolemol Amount of substancemolemol For info:The Kilogram is defined as the mass a platinum-iridium cylinder kept in Sevres, France The Second is based on time taken for a number of vibrations in a cesium atom (9.1 x 10 9 ).

SI Units Derived Units: If a units requires the use of more than one fundamental unit it is a derived unit. Derived Units: If a units requires the use of more than one fundamental unit it is a derived unit. For example: The Newton is a derived unit, because it is defined as the force required to accelerate 1kg at 1 ms-2. For example: The Newton is a derived unit, because it is defined as the force required to accelerate 1kg at 1 ms-2. Other derived units include Power (work / time), Pressure (force per unit area) Other derived units include Power (work / time), Pressure (force per unit area) Can you think of two more? Can you think of two more? 1) Speed (Units?) 2) Density (Units?)

Scientific Prefixes Prefixes, abbreviations and values: Prefixes, abbreviations and values: tera = T = giga = G = 10 9 mega = M = 10 6 kilo = k =10 3 hecto = h = 10 2 deca = da = 10 1 deci = d = centi = c = milli = m = micro =  = nano = n = pico = p = femto = f =

Scientific Notation For dealing with big or small numbers we use scientific notation: For dealing with big or small numbers we use scientific notation: a) 15,000,000W can be written as 1.5x10 7 W b) s can be written as 4.75x10 -5 s It may be more appropriate to express (a) as 15x10 6 or 15MW and (b) as 47.5x10 -6 s or 47.5  s.