1.1. Measurements in physics SI system: an international agreement on standard units Based on 7 basic units: http://www.zmescience.com/other/map-of-countries-officially-not-using-the-metric-system/ (180917) Quantity Unit Length s meter m Time t second Mass kilogram* kg Electric current I Ampere A Temperature T Kelvin K Ammount of substance n mole mol Luminous intensity candela cd ∗the only basic SI unit with a prefix All other are derived units (combinations of the basic units) Quantity Unit Velocity v Meters per second m s-1 Force F Newton (= kilogram meters per second squared) N (= kg m s-2)

We often need to convert between SI-units and other units Ex. 1: a) how many meters are 2 ft? b) how many feet are 2 meters? (1 ft = 0.305 m) Ex. 2: How many km/h is 45 mph? (1 mile = 1609 m)

When dealing with large or small numbers we can use Prefixes (metric multipliers) Powers of ten (scientific notation) Ex. 3: Write 102030405 m a) with a prefix b) in sci. not.

Rounding: Never round before you get your final answer! Always round your final answer! Round according to weakest link of input Mult/div: number of significant figures (Add/sub: least number of decimal places) (Final number 5 rounded up if number before is odd) 3.55 ≈ 3.6, 3.65 ≈ 3.6 Order of magnitude estimation: round to nearest power of ten for quick calculations Ex: How many times will your heart beat?