The Nature of ScienceSection 2: Standards of Measurement

Units and Standards

A standard is an exact quantity that people agree to use to compare measurements.

A standard is always exactly the same quantity when it is used anywhere in the world.

Measurement Systems

A measurement is a way to describe the world using numbers.

For a measurement to make sense it must include a number and a unit.

The metric system of measurement is based on multiples of ten.

The International System of Units (SI) In 1960, the International System of

Units was developed as an improvement to the metric system of measurement.

This system is abbreviated SI form the French Le Systeme Internationale d’Unites.

SI Base Units Each type SI measurement has a

base unit

There are seven (7) base units used in the SI system of measurement.Quantity

MeasuredUnit Symb

olLength Meter mMass Kilogra

mkg

Time Second sElectric current Ampere ATemperature kelvin KAmount of substance

Mole mol

Intensity of light Candela

cd

SI Prefixes

The SI system is easy to use because it is based on multiples of ten.

A prefix is added to the name of the base unit to indicate how many multiples of ten it should include.

Prefix Symbol

Value

Kilo k 1,000Deci d 0.1Centi c 0.01Milli m 0.001Micro µ 0.000 001Nano n 0.000 000

001

Quick review What is science? What is a standard? What are the three (3) major categories of

science? Upon which numeric multiple is the metric

system based? How does science explain God? Name the seven (7) base units in the SI system. Identify three (3) ways of investigating the

natural world. How many nanoseconds are in 2 seconds of

time?

Measuring Distance

In science, the word length is used to describe the distance between two points.

Metric rulers and metersticks are commonly used to measure length.

A meterstick is a little bit longer than a yardstick.

Choosing a Unit of Length The unit you

choose will depend on the object being measured.

By choosing the best unit, you can avoid very large or very small numbers.

Measuring Volume

Volume is the amount of space an object fills.

The volume of a rectangular solid, such as a brick, is found by multiplying its length, width, and height (V=l x w x h).

Volume is expressed as a “cubic” amount.

Practice Measuring Regular Volume What is the volume of a 2m x 3m

x4m moving truck?

Write the formula: (V= l x w x h)

Substitute given values: (V=2m x 3m x 4m)

Solve the equation: 24m3

Measuring the Volume of a Liquid To measure the volume of a liquid,

you first must know how much liquid the container can hold.

Liquid is commonly measured in liters and milliliters.

1 milliliter = 1 cm3

Do you remember? What is an independent variable?

Why is the dependent variable measured instead of the independent variable?

What is the volume of a brick that has a length of 20 cm, a width of 6 cm, and a height of 5 cm?

What are the most common units for expressing the volume of liquids?

Measuring Matter Mass is the

measure of how much matter is in an object.

You can determine mass by using a balance.

About Triple Beam Balances A triple-beam

balance gets its name because it has three beams that allow you to move known masses along the beam.

Because a triple beam balance compares a known mass to an unknown mass it is unaffected by gravity. Unlike a spring scale which really measures weight, the triple beam balance gives a true measure of mass.

Density: Another Mass MeasureDensity is the amount of mass in

one cubic unit of volume of an object.

Density = mass/volume

If two objects are the same size and one object has a greater mass, it also has a greater density.

Practice Calculating Density Suppose an object weight 15 g and has

a volume of 5 cm3. What is the density of the object?

Write the formula: D=m/v

Substitute given values: D=15 g/5 cm3

Solve the equation: 3 g/cm3

Measuring Time

Scientists need to keep track of how long it takes something to happen.

The unit of time in the SI system is second.

Measuring Temperature

Commonly think of temperature as how hot/cold something is . . .

Three scales for measuring temperature

A. FahrenheitB. CelsiusC. Kelvin

Fahrenheit Scale

Based on the temperature of the human body at 98.6º

Water freezes at 32º

Water boils at 212º

Celsius Scale

Scientists use the Celsius scale to measure temperature.

Water freezes at 0ºC

Water boils at 100ºC

The scale is divided evenly into 100 degrees between freezing and boiling.

Kelvin Scale

SI for measuring temperature is kelvin (K).

0ºK is called absolute zero.

0ºK = -273ºC

Divisions on the Kelvin scale are the same as the Celsius scale.

Think about it . . .Sharon used a push-machine to thrust a basketball and a volleyball across a football field. The volleyball went farther than the basketball 9 out of 10 times.1. What is the IV? DV? Constant

(controlled variables)?2. What can Sharon conclude about the

density of the basketball? Why?3. What other measurements can Sharon

take to support her conclusions?