1 Chapter 2 Analyzing Data Section 2.1 Units and Measurement Essential Questions: What are some SI base units and derived units How does adding a prefix change a unit. Base unit Second Meter Kilogram Kelvin Derived unit Liter density

2 “Walk five in that direction” All measurements depend on units that serve as reference standards ? ? The standards of measurements used in science are those of the metric system. All units are based on 10 or multiples of 10, which makes it simple to use. The International System of Units (SI) “Systeme Internationale d’Unites” is a revised version of the metric system (1960). It allows scientists to report data to other scientists worldwide.

3 SI base units Derived units are volume, density, pressure, energy etc. There are seven SI base unit, from which all other units are derived.

4 A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world and is independent of other units A second is defined as the frequency of the radiation given off by a Cesium-133 atom. Meter is defined by the distance light travels in a small fraction of a second in vacuum (space containing no matter) The standard kilogram (a platinum and Iridium cylinder) is kept in France in a vacuum under a triple bell jar. Temperature (Kelvin) is the quantitative measurement of the kinetic energy of particles.

5 Temperature Scales Metric Unit for Temperature is Degree Celsius (reference points: boiling point and freezing point of water) SI Unit for Temperature is Kelvin without degree sign (reference points is absolute zero = -273 °C) Conversion: K= °C °C = K Kelvin of water °C Freezing point 273K Celsius 100°C Boiling point 373K 100 divisions

66 Conversions: Kelvin and Celsius K= °C °C = K – 273 Convert 37°C to KConvert 150 K to °C Conversions: Fahrenheit and Celsius F = 1.8(°C) + 32 °C = (F – 32) x 5/9 Convert 37°C to F Convert 150 F to °C

7 Sometimes non-SI units are still preferred for practical reasons. (metric but not SI) Examples are liter for volume degree Celsius for temperature atmosphere or millimeter of mercury for pressure calorie for energy

8 Commonly Used Prefixes in the Metric System Examples: 1 km = 1000 m = 1 x 10 3 m 1 mg = 0.001g = 1 x g 1  g = g = 1 x g

9 Metric Units of Length 5 mm = ? m 5 km = ? m 5 nm = ? m = m (move decimal place three times) = m ( “ “ “ “ to the right) = m = 5 x m

10 1 meter  1.1 yard or 3.2 ft;height from floor to door knob 1 mile  1.6 km 1 km about 5 City blocks 1 dm  4 inches; the diameter of an orange 1 inch = 2.54 cm 1 cm  length of each side of a sugar cube 1  m  diameter of bacterial cell 1 nm  thickness of RNA molecule

The space occupied by any sample of matter is called its volume. (length x height x width for a cube) => m x m x m = m 3 cubic meter; e.g. size of dishwasher More convenient is liter (L), a non-SI unit 1 L = 10cm x 10cm 10cm = 1000 cm 3 11 Units of Volume 1 mL 1 L 1 qt

12 Laboratory Glassware used to measure volume Erlenmeyer Buret Graduated beaker Volumetric flask cylinder Flask

13 Units of Mass Mass is a measure of the quantity of matter, constant, regardless of its location Weight is a force of gravity exerted on a given mass, which varies depending on its location 1 kg is 1 L of liquid water at 4 °C or 1 g is 1 cm 3 of liquid water at 4 °C

14 Density Density is the ratio of the mass of an object to its volume mass m Density = = ---- volume V Density depends only on the composition of a substance, not on the size of the sample D =

15 Relationship Between Volume and Density

16 density decreases with increase in temperature Usually the density decreases with increase in temperature and a substance has a higher density in the solid state than as a liquid. Ice/cold water What is the exception? As a gas or vapor every substance has a lower density compared to its liquid and solid states. Calculation examples: A copper Penny has a mass of 3.1g and a volume of 0.35 cm 3. What is the density of copper? If piece of rock has a density of 5.85 g/cm 3 and a mass of 117g, what is its volume? Which unit?

17 density of substance (g/cm 3 ) Specific Gravity = density of water (g/cm 3) Hydrometer weight Liquid being measured Specific gravity read here