Physical Quantities and Units

Physical Quantities and UnitsAs/A Level Physics @ferrytanoto

Physical QuantityIs a feature of something which can be measured, e.g. length, weight, or time of fall.

Every physical quantity has a numerical value (magnitude) and a unit, e.g. 25 m is the physical quantity of length; 25 is the magnitude and metre is the unit.

PrefixPrefixSymbolMultiplying FactorPetaP1015TeraT1012GigaG109MegaM106Kilok103Decid10-1centic10-2Millim10-3Micro10-6Nanon10-9Picop10-12

Unit Conversion for Areas and VolumesLength1 mm = 10-3mAreasSquaring both sides 1 mm2 = (10-3)2 m2 = 10-6 m2

VolumeCubing both sides 1 mm3 = (10-3)3 m3 = 10-9 m3

Base UnitsQuantityUnitSymbolMassKilogramKgLengthMetremTimeSecondsElectric currentAmpere (amp)AThermodynamic temperatureKelvinKAmount of substanceMolemolLuminous intensitycandelacd

Derived Units consists of some combination of the base units. The base units may be multiplied together or divided by one another, but never added or subtracted

Derived UnitsQuantityUnitDerived unitFrequencyHertz (Hz)s-1Speedms-1m s-1Accelerationms-2ms-2ForceNewton (N)kgms-2EnergyJoule (J)kgm2s-2PowerWatt (W)kgm2s-3Electric chargeCoulomb (C)AsPotential differenceVolt (V)kgm2s-3A-1Electrical resistanceOhm ()kgm2s-3A-2Specific heat capacityJkg-1K-1m2s-2K-1

In any equation where each term has the same base units, the equation is said to be homogeneous or balanced.

A quantity which can be described fully by giving its magnitude is known as a scalar quantity.

A vector quantity has magnitude and direction.

Scalar and Vector QuantitiesQuantityScalarVectorMassWeightSpeedVelocityForcePressureElectric currentTemperature

Vector RepresentationOne way to represent a vector is by means of an arrow. The direction of the arrow is the direction of the vector quantity. The length of the arrow, drawn to scale, represents its magnitude.

Addition of VectorsThe combined effect of two (or more) vectors is called the resultant.Coplanar (all in the same plane) vectors may be added (or subtracted) using a vector diagram.The resultant may be found using a scale drawing of the vector diagram of by calculation.

Resolution of VectorsA single vector may be divided into two separate components.The dividing of a vector into components is known as the resolution of the vector.In general, a vector is resolved into two components at right-angles to each other.

Sine rule

Cosine rule

Pythagoras TheoremHypotenuse2 = Opposite2 + Adjacent2