Need for the Determination of Air Density Air is dense A cubic metre of air weighs approximately 12 kilograms A 1 kilogram stainless steel weight displaces 150 mg of air The density of air can vary between about 11 kg m 3 and 13 kg m 3 which is equi ID: 29891
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The National Physical Laboratory is operated on behalf of the DTI by NPL Management Limited,a wholly owned subsidiary of Serco recommendations of good massmeasurement practice in calculatingair density and buoyancy correctionsbut should not be considered acomprehensive guide.Air is denseA cubic metre of air weighsapproximately 1.2 kilogramsA 1 kilogram stainless steelabout 1.1 kg m (P) - h(0.00252t- 0.020582)](273.15 + t)WhereAD = Air density (kg mP = Air pressure (mbar)h= Relative humidity oft = Air temperature (¡C)There is a typical uncertainty of 4 parts indensity of 1.2 kg m±10% Buoyancy Correction andIntroduction1Need for the Determination1What is the Typical Density 1Determination of Air 1Air Density Artefacts2 Variation in Buoyancy2Effect with VaryingWhen Should I make a 3Buoyancy Correction?How do I make a 3Buoyancy Correction?What do the OIML 3Conventional and4True MassRelated Good Practice4References4 Buoyancy Correction Note 5/2/03 10:07 am Page 2 4641/0.2k/SEA/0203 National Physical LaboratoryTeddington, Middlesex, TW11 0LWTel: 020 8943 6224 Website:www.npl.co.uk/npl/md/Conventional and True MassTrue massA measure of the amount of substance of an artefactThe constant of proportionality between F and g (F=mg)Measured by comparison between the masses of artefacts (and defined by the massof the international prototype kilogram)Conventional MassFor a weight taken at 20 ¡C, the conventional value of mass is the mass of a reference Page - 4 Buoyancy Correction Note 5/2/03 10:07 am Page 1