Numbers and Measurements Measurement – the determination of a physical property of the sample of interest Dimension (length, width, height) Mass Capacity (how many marbles will fit in this box?) Quantity Accuracy How close a measurement comes to the true value Precision How close a series of measurements are to each other

Numbers and Measurements Good Accuracy Good Precision Accuracy How close a measurement comes to the true value Precision How close a series of measurements are to each other Poor Accuracy Good Precision Poor Accuracy Poor Precision

Numbers and Units Measurements always contain: Number, Uncertainty and a UNIT Measurable value Standard against which the quantity is compared. Error in measured value Internationally accepted system of measurements is called the Systéme Internationale dUnités (SI)

Error in Measurements All measurements have uncertainty Thermometer A 45 ± 2 ˚C Thermometer B 44.7 ± 0.1

Significant Figures Numbers in any measurement that are known with certainty with one more number that is uncertain Thermometer A 45 ± 2 ˚C Thermometer B 44.7 ± significant figures 3 significant figures

Significant Figures Rule 1 Non-zeroes are ALWAYS significant Rule 2 Leading zeroes are NEVER significant Rule 3 Confined zeroes are ALWAYS significant Rule 4 Trailing zeroes are significant IF they accompany decimal point