Uncertainty in measurement, significant figures, rounding and calculations

1. Uncertainty in measurement, significant figures, rounding and calculations

2. 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.

3. 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

4. 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”

5. 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

6. 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

7. 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

8. dimensional analysis • hand-out