DATA

There is no such thing as absolute certainty of a scientific claim. The validity of a scientific conclusion is always limited by: the experiment the experiment design, equipment, etc... the experimenter the experimenter human error, interpretation, etc... our limited knowledge our limited knowledge ignorance, future discoveries, etc...

developed in France in 1795 a.k.a. “SI”-International System of Units a.k.a. “SI” - International System of Units The U.S. was (and still is) reluctant to “go metric.” very costly to change very costly to change perception of “Communist” system perception of “Communist” system natural resistance to change natural resistance to change American pride American pride

The SI unit of: length is the meter, m length is the meter, m time is the second, s time is the second, s mass is the kilogram, kg. mass is the kilogram, kg. electric charge is the Coulomb, C electric charge is the Coulomb, C temperature is the degree Kelvin, K temperature is the degree Kelvin, K an amount of a substance is the mole, mol an amount of a substance is the mole, mol luminous intensity is the candle, cd luminous intensity is the candle, cd

The second is defined in terms of The second is defined in terms of atomic vibrations of Cesium-133 atoms. The meter is defined in terms of the speed of light. The meter is defined in terms of the speed of light. The kilogram is still defined by The kilogram is still defined by an official physical standard. “Derived units” are combinations of these “fundamental units” Examples include speed in m/s, area in m 2, force in kg. m/s 2, acceleration in m/s 2, volume in m 3, energy in kg. m 2 /s 2

10 18 exa E peta P tera T 10 9 giga G 10 9 giga G 10 6 mega M 10 6 mega M 10 3 kilo k 10 3 kilo k 10 2 hecto h 10 2 hecto h 10 1 deka da 10 1 deka da 10  18 atto a 10  15 femto f 10  12 pico p 10  9 nano n 10  9 nano n 10  6 micro  10  6 micro  10  3 milli m 10  3 milli m 10  2 centi c 10  2 centi c 10  1 deci d 10  1 deci d

Explore the metric system at link1, link2, and link3. link1link2link3link1link2link3 See definitions of metric units here. here Click here to do conversions. here

All measurements have some degree of uncertainty. Precision single measurement exactness, definiteness single measurement - exactness, definiteness group of measurements agreement, closeness together group of measurements - agreement, closeness together Accuracy closeness to the accepted value % error = accepted - observed accepted x 100%

Four student lab groups performed data collection activities in order to determine the resistance of some unknown resistor (you will do this later in the course). Data from 5 trials are displayed below. Suppose the accepted value for the resistance is 500 Ω. Then we would classify each groups’ trials as: Group 1: neither precise nor accurate Group 2: precise, but not accurate Group 3: accurate, but not precise Group 4: both precise and accurate Example of the differences between precision and accuracy for a set of measurements: Group Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 avg

1. All non-zero digits are significant. 2. Zeros between other significant digits are significant. 3. Leading zeros are not significant. 4. Final zeros before the decimal are not significant.

Operations with Significant Digits Addition and Subtraction round the sum or difference to the least precise decimal place Multiplication and Division round so that the product or quotient has a total number of significant digits equal to the total number of significant digits of the least precise quantity

Learn more about significant digits herehere and here. here Check your understanding here and here. here The “bottom line” is that the precision to which a measured or calculated amount is written provides valuable information as to the precision (certainty) of that value and the device used to measure it.