90 likes | 308 Views
Uncertainty in measurement, significant figures, rounding and calculations. Uncertainty in measurement. Every measurement device has its limitations You can only estimate to between the lines, but not beyond. Eg : a bathroom scale doesn’t give your weight to the thousandth of a pound
E N D
Uncertainty in measurement, significant figures, rounding and calculations
Uncertainty in measurement • Every measurement device has its limitations • You can only estimate to between the lines, but not beyond. • Eg: a bathroom scale doesn’t give your weight to the thousandth of a pound • Eg: diagram in book, p 133 • So we can only record measurements to the next level between the lines we can see, because we cannot visually estimate further.
Uncertainty in measurement • A beaker is never an accurate measurement device. • For accurate liquid measurement, use a… • Graduated cylinder • The liquid in a graduated cylinder may form a curve, called a … • Meniscus • When reading a graduated cylinder, always read the _______ of the meniscus • bottom
Conversions: Celsius to Kelvin • Water freezes at 32˚F and boils at 212 ˚F • Water freezes at 0˚C and boils at 100˚C • As things cool down, particles slow down • The Kelvin temperature scale is based on absolute zero – a theoretical temperature at which electrons stop moving around nuclei and matter stands still • There is no such thing as a negative Kelvin • Kelvin is not stated as “degrees Kelvin”, but simply as “Kelvin”
Conversions: Celsius to Kelvin • Each Kelvin unit is exactly equal to one Celsius degree. • 0 Kelvin = -273˚C • Therefore 0˚C = 273 K • Add 273 degrees to Celsius to get Kelvin • Try these: • 244 Kelvin = _______ Celsius • -29 • Water boils at ________ Kelvin • 373 • Water freezes at ________ Kelvin • 273
Density (p. 159) • How “packed” something is. • Loosely “packed” = low density • Tightly packed = high density • A derived unit. To calculate… • Mass ÷ volume • We love density • D = m/v • m = … • vd • v = … • m/d
specific gravity • compares the density of something to the density of water at 4˚C (when water is the most dense) • specific gravity of water at 4˚C is 1.0 • so, if an object floats, its specific gravity is (less than or greater than) 1?... • less than 1 • if an object sinks, its specific gravity is > 1
dimensional analysis • hand-out