Chapter 2-2 Units of Measurement Modification of Mrs. Rugh’s presentation 9/22/14

Measurements are information that represent quantities. Measurement is different from Quantity

A quantity is something that has size, magnitude, or amount. Measurements A quantity is something that has size, magnitude, or amount. Example: 1 teaspoon Unit of measurement Measurement Quantity is volume

Measurement Standards Le Systeme International d’Unites (SI) Adopted in 1960 by the General Conference on Weights and Measures. Now used and agreed upon by scientists around the world. This is basically what we call the “metric” system

Not all units in this book are SI units SI system Has 7 “base units” Most other units are derived from combinations of 2 or more “base units” Not all units in this book are SI units

Measurement Standards SI Units are defined in terms of standards of measurements. In 1795 the meter was defined as one ten-millionth of the distance from the Earth's equator to the North Pole (at sea level) Before 1927 the official meter was defined by the length of a platinum-iridium bar kept in France. Since 1983, the meter has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second."[2]

Measurement Standards Kilogram is the base unit of mass and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK). It is the only SI unit that is still defined by an artifact instead of a physical property. However, there is discussion to define the kilogram in terms of a fundamental constant of nature.

Measurement Standards The second is the base unit of time Since 1967, the second has been defined to be: the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[

SI Base Units Quantity Unit Unit Quantity symbol name abbreviation Length l meter m Mass m gram g Time t second s Temperature T kelvin K Amount of n mole mol substance You have a handout with this information on it…

Mass ≠ Weight Mass is a measure of the amount of matter, weight depends on the local gravitational field. We usually measure mass with a balance, weight is usually measured with a spring scale. We will talk about MASS only in this class (leave weight for physics…

Prefixes –what do they MEAN The handout has the important prefixes you need to know on it. You should know the prefixes on the handout because you will use them…over and over…and over again.

Prefixes –what do they MEAN Come up with one example of what you might measure with each of these units in meters.

Which unit (with appropriate prefix) would you use to measure this stuff? Diameter of an atom Weight of an elephant Area of the Tacoma Dome Temperature of the summit of Mt. Rainier Temperature in outer space

Derived SI Units Derive v. Mathematics: Obtain (a function or equation) from another by a sequence of logical steps, for example by differentiation: the volume fraction of the soil can then be derived as a function of L Oxforddictionary.com

Length (m) x Length (m) = Area (m2) Derived SI Units derived units…units that are created by combining 2 or more SI Base Units (usually through multiplying or dividing base units). For example: Length (m) x Length (m) = Area (m2) Mass (kg)/Volume (m3) = Density (kg/m3)

Example: Volume The amount of space occupied by an object. Solids: m x m x m = m3 Liquids and gases: 1 Liter = 1 dm3 = 1000 cm3 So 1 mL = 1 cm3

The ratio of mass to volume, or mass divided by volume Density The ratio of mass to volume, or mass divided by volume D = mass/volume or D = m/v Often (though not always) expressed in units of g/cm3.

Quick Check Units of Measurement Quantity 5 ns Nanoseconds time 3.2 kg/L Kg/L density 0.88 pm Picometers length 540 km2 Square kilometers area 173 K Kelvin temperature 2 mm3 Cubic millimeters volume 6.02x1023 mol moles Amount of substance 5ns time 3.2 kg/L density 0.88 pm length 540 km2 area 173 K temperature 2 mm3 volume 23degC temperature

Now Do the Practice Problems Due tomorrow if you don’t finish in class…