Nature of
Science
LESSON 2
Methods of Science
Measurement and Scientific Tools
Key Concepts
• Why is it important for
scientists to use the
International System of
Units?
• What causes measurement
uncertainty?
• What are mean, median,
mode, and range?
Key Concept Check
1. Explain Why is it
important for scientists to
use the International System
of Units (SI)?
Imagine that a scientist is observing an erupting volcano.
He describes in his journal that the flowing lava is bright red
with a black crust, and it has a temperature of about 630°C.
A description is a spoken or written summary of observations.
There are two types of descriptions. A qualitative
description, such as bright red, uses senses (sight, sound, smell,
touch, taste) to describe an observation. A quantitative
description, such as 630°C, uses numbers and measurements
to describe an observation. Later, the scientist might explain
his observations. An explanation is an interpretation of
observations. Because the lava was bright red and about 630°C,
the scientist might explain the lava is cooling, and the
volcano did not recently erupt.
The International System of Units
At one time, scientists in different parts of the world used
different units of measurement. This made sharing scientific
information difficult. Imagine the confusion when a British
scientist measured weight in pounds-force and a Japanese
scientist measured in momme (MOM ee).
In 1960, scientists adopted a new system of measurement.
The International System of Units (SI) is the internationally accepted
system for measurement. SI uses standards of measurement,
called base units, shown in the table below.
SI Base Units
Interpreting Tables
2. Analyze Which unit is
used to measure temperature?
Quantity Measured
Unit
Symbol
Length
meter
m
Mass
kilogram
kg
Time
second
s
Electric current
ampere
A
Temperature
Kelvin
K
Amount of substance
mole
mol
candela
cd
Intensity of light
NOS 10
Methods of Science
Reading Essentials
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Building Vocabulary As you
read, underline the words and
phrases that you do not
understand. When you finish
reading, discuss these words
and phrases with another
student or your teacher.
Description and Explanation
SI Unit Prefixes
In addition to base units, SI uses prefixes to identify the
size of the unit, as shown in the table below. Prefixes are used
to indicate a fraction of ten or a multiple of ten. In other
words, each unit is either ten times smaller than the next
larger unit or ten times larger than the next smaller unit.
For example, the prefix deci– means 10-1, or 1/10. A decimeter
is 1/10 of a meter. The prefix kilo– means 103, or 1,000.
A kilometer is 1,000 m.
Prefixes
Prefix
Mega- (M)
Kilo- (k)
Meaning
1,000,000 (106)
1,000 (103)
Hecto- (h)
100 (102)
Deka- (da)
10 (101)
Deci- (d)
0.1 (10-1)
Centi- (c)
0.01 (10-2)
Milli- (m)
0.001 (10-3)
Micro- (μ)
0.000 001 (10-6)
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Converting Between SI Units
Because SI is based on ten, it is easy to convert from one
SI unit to another. To convert SI units, you must multiply or
divide by a factor of ten. You also can use proportions, as
shown in the Math Skills activity on this page.
Math Skills
A book has a mass of 1.1 kg.
Using a proportion, find the
mass of the book in grams.
a. Use the table to
determine the correct
relationship between the
units. One kg is 1,000
times greater than 1 g.
So, there are 1,000 g in
1 kg.
b. Then set up a proportion.
g
( 1.1xkg ) = ( 1,000
1 kg )
(1,000 g)(1.1 kg)
x=(
)
1 kg
= 1,100 g
c. Check your units. The
answer is 1,100 g.
3. Use Proportions Two
towns are separated by
15,328 m. What is the
distance in kilometers?
A dosage of medicine is
325 mg. What is the dosage
in grams?
Measurement and Uncertainty
Have you ever measured an object, such as a paper clip?
The tools used to take measurements can limit the accuracy
of the measurements. All measurements have some
uncertainty.
If you measured a paper clip with a ruler divided into
centimeters, you would know that the paper clip is between
4 cm and 5 cm, because only whole centimeters are shown.
You might guess that the paper clip is 4.5 cm long.
With a ruler that has measurements divided into
millimeters, you could say with more certainty that the
paper clip is about 4.7 cm long. This measurement is more
accurate than the first measurement.
Reading Essentials
Key Concept Check
4. Relate What causes
measurement uncertainty?
Methods of Science
NOS 11
Significant Digits and Rounding
Make a vertical two-tab book
to organize your notes about
SI conversions and rounding
significant digits.
Conversions
Between
SI Units
Rounding
Significant
Digits
Because scientists duplicate each other’s work, they must
record numbers with the same degree of precision as the
original data. Significant digits allow scientists to do this.
Significant digits are the number of digits in a measurement that you
know with a certain degree of reliability.
In order to achieve the same degree of precision as
a previous measurement, it often is necessary to round a
measurement to a certain number of significant digits.
Suppose you need to round the number below to four
significant digits.
1,348.527 g
To round to four significant digits, you need to round the
8. If the digit to the right of the 8 is 0, 1, 2, 3, or 4, the digit
being rounded (8) remains the same. If the digit to the right
of the 8 is 5, 6, 7, 8, or 9, the digit being rounded (8)
increases by one. The rounded number is 1,349 g.
Reading Check
Interpreting Tables
6. Assess Which zeros in a
number are not significant?
NOS 12
Methods of Science
Significant Digits Rules
All nonzero numbers are significant.
Zeros between nonzero digits are significant.
One or more final zeros used after the decimal point are significant.
Zeros used solely for spacing the decimal point are NOT significant.
The zeros only indicate the position of the decimal point.
Note: The bold numbers in the examples are the significant digits.
1.
2.
3.
4.
Number
Significant Digits
Applied Rules
1.234
4
1
1.02
3
1, 2
0.023
2
1, 4
0.200
3
1, 3
1,002
4
1, 2
3.07
3
1, 2
0.001
1
1, 4
0.012
2
1, 4
50,600
3
1, 2, 4
Reading Essentials
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5. Apply Round the
following number to the
place value shown in bold:
2,451.225
What if you need to round 1,348.527 g to two significant
digits? You would look at the number to the right of the 3 to
determine how to round. 1,348.527 rounded to two
significant digits would be 1,300 g. The 4 and 8 become
zeros. The table below shows some rules for expressing and
determining significant digits.
Mean, Median, Mode, and Range
A rain gauge measures the amount of rain that falls on a
location over a period of time. A rain gauge can be used to
collect data in scientific investigations, such as the data
shown in the table below. Scientists often need to analyze
their data to obtain information. Four values often used
when analyzing numbers are median, mean, mode, and
range.
Reading Check
7. State What values do
scientists often use when
evaluating data sets?
Rainfall Data
Month Order
Numerical Order
January
7.11 cm
1.47 cm
February
11.89 cm
7.11 cm
March
9.58 cm
7.11 cm
April
8.18 cm
8.18 cm
May
7.11 cm
8.84 cm
June
1.47 cm
9.58 cm
July
18.21 cm
11.89 cm
August
8.84 cm
18.21 cm
Interpreting Tables
8. Interpret Which month
had the lowest rainfall? the
highest rainfall?
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Median The median is the middle number in a data set when
the data are arranged in numerical order. The rainfall data are
listed in numerical order in the right column of the table
above. The items in bold are the two middle numbers. If you
have an even number of data items, add the two middle
numbers together and divide by two to find the median.
cm + 8.84 cm
_________________
median = 8.18
= 8.51 cm
2
Mean The mean, or average, of a data set is the sum of the
numbers in a data set divided by the number of entries in
the set. To find the mean, add the numbers in your data set
and then divide the total by the number of items in your
data set.
(sum of numbers)
mean = ________________
Key Concept Check
9. Summarize What are
median, mean, and mode?
(number of items)
72.39 cm
= _________
8 months
9.05 cm
= _______
month
Mode The mode of a data set is the number or item that
appears most often. The number 7.11 occurs twice. All other
numbers only appear once.
mode = 7.11
Reading Essentials
Methods of Science
NOS 13
Reading Check
10. Explain How do you
find the range for a data set?
Range The range is the difference between the greatest
number and the least number in the data set.
range = 18.21 - 1.47 = 16.74
Scientific Tools
As you engage in scientific inquiry, you will need tools to
help you take quantitative measurements. Always follow
appropriate safety procedures when using scientific tools.
Science Journal
Use a science journal to record observations, questions,
hypotheses, data, and conclusions from your scientific
investigations. A science journal is any notebook that you
use to take notes or record information and data while you
conduct a scientific investigation.
Reading Check
11. Define What is a
science journal? How is it
used?
Keep your journal organized so you can find information
easily. Write the date whenever you record new information
in the journal. Make sure you are recording your data
honestly and accurately.
Rulers and Metersticks
Use rulers and metersticks to measure lengths and
distances. The SI unit of measurement for length is the
meter (m).
To measure long distances, such as the distance between
cities, use an instrument that measures in kilometers. Be
careful when carrying rulers and metersticks, and never
point them at anyone.
Glassware
Reading Check
Use beakers to hold and pour liquids. The lines on a
beaker are not very precise measurements, so you should
use a graduated cylinder to measure the volume of a liquid.
Liquid volume is typically measured in liters (L) or
milliliters (mL).
12. Name Scientists
measure the volume of a
liquid in which units of
measure?
NOS 14
Methods of Science
Reading Essentials
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For small objects, such as pebbles or seeds, use a metric
ruler with centimeter and millimeter markings. To measure
larger objects, such as the length of your bedroom, use a
meterstick.
Triple-Beam Balance
Use a triple-beam balance to measure the mass of an
object. The mass of a small object is measured in grams. The
mass of a large object is usually measured in kilograms.
Triple-beam balances are instruments that require some
care during use. Follow your teacher’s instructions so that
you do not damage the instrument. Digital balances also
might be used.
Reading Check
13. Identify What can you
measure using a triple-beam
balance?
Thermometer
Use a thermometer to measure the temperature of a
substance. Although Kelvin is the SI unit for temperature,
you will use a thermometer to measure temperature in
degrees Celsius (°C).
To use a thermometer, place a room-temperature
thermometer into the substance for which you want to
measure temperature. Do not let the thermometer touch the
bottom of the container that holds the substance or you will
get an inaccurate reading.
Reading Check
14. State How will you
measure temperature when
conducting scientific
investigations?
When you finish, remember to place your thermometer
in a secure place. Do not lay it on a table, because it can roll
off the table. Never use a thermometer as a stirring rod.
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Computers and the Internet
Use a computer to collect, organize, and store information
about a research topic or scientific investigation. Computers
are useful tools to scientists for several reasons.
Scientists use computers to record and analyze data and
to research new information. They also can quickly share
their results with others worldwide over the Internet.
Reading Check
15. Consider How do
scientists use computers
and the Internet?
Reading Essentials
Methods of Science
NOS 15
Tools Used by Earth Scientists
Binoculars
Reading Check
16. Describe how
scientists might use
binoculars.
Binoculars are instruments that enable people to view
faraway objects more clearly. Earth scientists use them to
view distant landforms, animals, or even incoming
weather.
Compass
A compass is an instrument that shows magnetic north.
Earth scientists use compasses to navigate when they are in
the field and to determine the direction of distant landforms
or other natural objects.
Wind Vane and Anemometer
A wind vane is a device, often attached to the roof of a
building, that rotates to show the direction of the wind. An
anemometer, or wind-speed gauge, is used to measure the
speed and the force of wind.
Streak Plate
Reading Check
A streak plate is a piece of hard, unglazed porcelain that
helps you identify minerals. When you scrape a mineral
along a streak plate, the mineral leaves behind powdery
marks. The color of the mark is the mineral’s streak.
17. Point Out How do
scientists use a streak plate?
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NOS 16
Methods of Science
Reading Essentials
Mini Glossary
description: a spoken or written summary of observations
explanation: an interpretation of observations
significant digits: the number of digits in a measurement
that are known with a certain degree of reliability
International System of Units (SI): the internationally
accepted system for measurement
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that
explains how a scientific description and explanation are related.
2. Complete the following table to describe SI base units.
Unit
Quantity Measured
kilogram
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
time
Kelvin
electric current
candela
3. Explain the difference between qualitative and quantitative descriptions.
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Methods of Science
END OF
LESSON
NOS 17