Physics – an experimental science Physis (greek) means nature We make models and use measurements to verify (or falsify) them

Make groups Measure the length of the corridor

Measurements and uncertainty The result of a measurement is a value AND a unit Always give a reasonable precision 176.8 cm (four significant figures) 177 cm (three s.f.) 180 cm (two s.f.) If possible, give the measurement error 5.0 ± 0.5 cm (absolute error) 5.0 ± 10% cm (relative error)

SI-system SI system: an international agreement on standard units Based on 7 basic units 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 Powers of ten Ex. 3: Write 12300000 m with: a) a prefix b) with a power of 10

In groups of 6-7: one drops a piece of paper, all the others time the fall. Save your results

Spreadsheets and graphs Spreadsheets are used to calculate the average and an error for repeted measurements Graphs are used to find patterns in connected measurements Show clear data points (NEVER play ”connect the dots”!) Add a line of best fit If possible, show error bars

Important tools: Task: measure the Vernier calipers Micrometer Stopwatch Task: measure the thickness of your hair width of your shoe time it takes for a shoe to fall from desk to floor