Chapter 2-2Units of

Measurement

Modification of Mrs. Rugh’s presentation 9/22/14

Measurements

Measurements are information that represent quantities.

Measurement is different from Quantity

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

SI systemHas 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 StandardsSI 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 StandardsKilogram 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 timeSince 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 mMass m gram gTime t second sTemperature T kelvin KAmount 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

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

Density

The ratio of mass to volume, or mass divided by volume

D = mass/volume or D = m/vOften (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

Now Do the Practice Problems

Due tomorrow if you don’t finish in class…