How much? How long? How many? Measurement How much? How long? How many?

Exact and inexact numbers A number with no uncertainty it A dozen donuts, seven students, etc. Inexact number: A number that has a degree of uncertainty in it; results anytime a measurement is made Height of student; temperature of student

Precision and Accuracy How close a measured value is to the actual (true) value Precision: How close the measured values are to each other

Testing our knowledge How accurate? How Precise? Low accuracy High precision

Testing our knowledge How accurate? How Precise? High accuracy Low precision

Testing our knowledge How accurate? How Precise? High accuracy High precision

Systems of Measurement English: Commonly used in commerce and homes Inch, foot, pound, quart, and gallon Metric system Used worldwide SI system Revised in 1960 with improved units SI stands for “French Systeme International d’Unites” Used by scientists

SI System Meter m gram g Second s kelvin K mole ampere A candela cd The Seven Base Units in the SI system: Base quantity Unit Name Unit Abbreviation Length Meter m Mass gram g Time Second s Temperature kelvin K Amount of substance mole Electric current ampere A Luminous intensity candela cd

Metric system prefixes Common prefixes For example, 100 cm = 1 m 1,000 mg = 1 gm Kilo k 1,000 Deci d 1/10 Centi c 1/100 Milli m 1/1,000

Length Meter is the SI base unit of length 1 meter=1.05 yards A dime is about 1 mm thick Or…1/1000 of a m Your little finger is about 1 cm across Or…1/100 of a m

Mass vs. Weight Mass Weight A measure of the total quantity of matter in an object Weight A measure of the force exerted on an object by gravitational forces If you weigh 60 kg on Earth, will you weigh more or less on the moon? Why?

Mass vs. Weight How much does this astronaut floating in space weigh? What is the astronaut’s mass?

Mass Kilogram is the SI unit for mass Note that the prefixes are added to gram not kilogram, i.e., centigram, milligram, etc. 10 pennies weigh about 1 gram 1 gram is 1/1,000 kilogram Aspirin commonly is 325 mg 1 milligram = 1/1000 gram

Area and volume Area: measure of extent of a surface For a square, length vs width Square feet, ft2 Square cm, cm2 Volume: measure of the amount of space occupied by an object For a cube, side x side x side Cubic feet, ft3 Cubic cm, cm3

Volume Cubic meter (m3) is the SI system base unit for volume A m3 is too large to be used in the chemistry lab, so cm3 is much more common 1 cubic cm (cm3 )= 1 milliliter (ml) 1 liter is a volume equivalent to that of a cube that is 10 cm x 10 cm x 10 cm or 1,000 cm3

SI Units The best way to understand SI units is to use them in everyday life Everyday examples

Measuring volume Technique for measuring volume

Temperature A measure of the hotness or coldness of an object Three scales: Kelvin after William Kelvin (1824-1907) Does not use degree symbol Celsius After Anders Celsius (1701-1744) Most commonly used in science

Three scales Kelvin Celsius Fahrenheit after British mathematician and physicist, William Kelvin (1824-1907) Does not use degree symbol No negative numbers Celsius after Swedish astronomer, Anders Celsius (1701-1744) Most commonly used in science Fahrenheit After German physicist, Gabriel Fahrenheit (1686-1736) Based on the temperature of a salt-ice mixture as 0°F and the boiling point of mercury at 600°F

Common temperatures Freezing point of water Room temperature 0°C=32°F=273.15 K Room temperature 22°C=72°F=295 K Boiling point of water 100°C=212°F=373 K