Measurements in physics

SI System The seven basic SI units are: 1.The metre (m) 2.The kilogram (kg) 3.The second (s) 4.The Ampere (A) 5.The kelvin (K) 6.The mole (mol) 7.The candela (cd)

Common prefixes

Significant digits The rules for significant figures are as follows: The leftmost non-zero digit is significant and is in fact the most significant digit in the number. If the number has no decimal point, the rightmost non-zero digit is significant and is in fact the least significant. If the number does have a decimal point, the least significant digit is the rightmost digit (which may be zero). The number of significant digits of a number is the number of digits from the most to the least significant. In multiplication or division (or raising a number to a power or taking a root) the result must have as many significant digits as those of the number with the least significant digits entering the operation.

Orders of magnitude What is the mass of the sun? What is the mass of an atom? What is the size of the universe? What is the size of a virus?

Some interesting sizes Length/m Distance to edge of observable universe10 26 Distance to the Andromeda galaxy10 22 Diameter of the Milky Way galaxy10 21 Distance to nearest star10 16 Diameter of solar system10 13 Distance to sun10 11 Radius of the earth10 7 Size of a cell10 -5 Size of a hydrogen atom Size of a nucleus Size of a proton10 -17

Some interesting masses Mass/kg The universe10 53 The Milky Way galaxy10 41 The sun10 30 The earth10 24 Boeing 747 (empty)10 5 An apple10 -1 A raindrop10 -6 A bacterium Smallest virus A hydrogen atom An electron10 -30

Some interesting time intervals Time/s Age of the universe10 17 Age of the Earth10 17 Time of travel by light to nearby star10 8 One year10 7 One day10 5 Period of a heartbit1 Period of red light Time of passage of light across a nucleus10 -24