Name
CHAPTER 1
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Date
Introduction to Science
SECTION
1 The Nature of Science
KEY IDEAS
As you read this section, keep these questions in mind:
• What processes do scientists use to answer questions?
• How is a scientific theory supported by evidence?
• How do scientists use math and models to represent
ideas?
What Is Science?
When you have a question about how something
works, how do you find the answer? People from all parts
of the world use science to answer questions. Science
is the different processes that people use to discover
how things work in the natural world. Science is also the
knowledge that people gain about the natural world by
using scientific processes. Some examples of scientific
processes are shown in the table below.
Scientific Process
Examples
Investigating
learning about an object or event by watching,
measuring, testing, or reading other scientists’ work
Experimenting
setting up a planned, controlled test to find out how
something reacts to a change
Observing
carefully watching, measuring, and writing down
information about an object or an event
Confirming results
repeating observations and experiments to see
whether the results are the same
People who do science are called scientists. Many
scientists perform experiments. An experiment is a
careful test of the way something reacts to a change. A
scientist may perform experiments to describe a newly
discovered feature of the natural world. Some scientists
perform experiments to help explain a natural event.
Scientists also perform experiments to check the results
of other experiments.
Scientists who do experiments to learn more about the
world are doing pure science. However, many people use
science in other ways. Technology is the application of
science for practical uses. Advances in science and technology depend on one another.
READING TOOLBOX
Summarize As you read,
underline important ideas
about scientific theories.
When you are finished reading, write a short summary of
scientific theories using the
underlined ideas.
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Brainstorm In a small
group, talk about ways that
you use scientific processes
in your everyday life.
READING CHECK
1. Identify What are three
reasons scientists carry out
experiments?
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The Nature of Science continued
How Do Scientists Learn About the World?
Many scientists use experiments to learn about the
natural world. For example, in 1895 a German scientist
named Wilhelm Roentgen experimented with a newly
discovered form of energy. At that time, scientists were
learning about this new form of energy. Scientists first
discovered this kind of ray when they passed electricity
through tubes like the one shown below.
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Metal rod
Metal rod
Research Learn more about
cathode rays, Roentgen, or
another historic scientific
discovery. Share what you
learn with a partner or a
small group.
READING CHECK
2. Identify What did
Roentgen think was the
reason that other scientists
did not see the cardboard
glowing?
The tube contained two metal rods that were separated
from each other. Scientists removed all of the air from
the tube. Then, they connected the rods to an electrical
source. Electric charges flowed through the empty space
between the rods and produced the rays. Scientists called
these rays cathode rays.
Roentgen learned about cathode rays from the work of
other scientists. He knew that cathode rays could make
certain minerals glow. Scientists used pieces of cardboard coated with powder made from these minerals to
detect, or find, the rays.
Some scientists had carried out experiments to learn
whether cathode rays could pass through different materials. They learned that cathode rays could pass through
thin metal foil. They also learned that cathode rays could
travel only a few centimeters through the air.
Scientists had also tried to find out whether cathode
rays could travel through glass. They tried to detect
the rays outside of the tube using the mineral-coated
cardboard. They did not see the cardboard glow.
However, Roentgen thought that bright light from
inside the tube might have kept them from seeing the
cardboard glow. He decided to carry out an experiment
to test this idea.
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The Nature of Science continued
EXPERIMENTING AND CONFIRMING RESULTS
Roentgen planned his experiment carefully. First, he
covered the tube with heavy black paper. He thought that
the paper would block any light from inside the tube.
Next, he turned off the lights in the room and turned on
the electricity in the tube. He did this to check that no
light was passing through the paper.
When Roentgen turned on the tube, he noticed something he didn’t expect. The cardboard detector was glowing. However, the cardboard was more than 1 m away
from the tube. Roentgen knew that cathode rays could
not travel that far through the air. He hypothesized that
the tube was producing rays other than cathode rays. He
thought these were a new kind of ray that no one had
seen before.
Roentgen’s results were unexpected. He repeated his
experiment to find out whether he would get the same
results. He set up the experiment exactly as before, and
held the cardboard detector 1 m away from the tube.
Again, the cardboard glowed. His results were confirmed.
Roentgen’s results helped him to think of new questions. He carried out more experiments to find answers
to these questions. For example, he tried holding his
hand in the path of the rays. The bones in his hand made
shadows on the cardboard detector. The rays could pass
through his skin, but not through the bones.
Roentgen called the new rays X rays. He found that
X rays passed through almost everything. Roentgen
included an X ray of his wife’s hand in one of the first
papers that he published on X rays. That image is
shown below.
READING CHECK
3. Explain Why did
Roentgen cover the tube
with heavy paper?
READING CHECK
4. Describe What made
Roentgen think that the tube
was producing rays other
than cathode rays?
EHHDBG@<EHL>K
X rays pass through skin and
muscle, but not through bone
or metal. The dark object on the
second finger of Roentgen’s wife’s
hand is her wedding ring.
5. Infer What do you think is
the reason Roentgen’s wife’s
wedding ring appears on the
X ray, but her fingernails do
not?
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The Nature of Science continued
What Is a Scientific Law?
READING CHECK
Scientists like Roentgen may carry out experiments to
learn how things behave. In some cases, scientists can
use the results of experiments to predict what will happen in other situations. In those cases, the result of an
experiment may be considered a scientific law.
A scientific law is a statement or equation that accurately describes a natural process. For example, one scientific law states that warm objects become cooler when
they are placed in cooler surroundings. An example of
this is shown below.
6. Define What is a
scientific law?
²#
²#
A hot cooking pot always cools when it is moved from a hot stove to a
cooler counter top.
Scientists can use scientific laws to make predictions.
A prediction is an idea about what will happen in the
future. However, a law does not explain how a process
takes place. For example, the law that states that warm
objects cool off does not explain why they cool off. To
explain why an event happens, scientists use scientific
theories.
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7. Compare What is the
main difference between a
scientific theory and a
scientific law?
What Is a Scientific Theory?
In everyday speech, people often use the word theory
to mean “guess.” However, in science, a theory is much
more than a guess. A scientific theory is a system of
ideas that explains many related observations. Scientific
theories are supported by many observations.
The theory that explains why warm objects cool down
is called the kinetic theory of energy. This theory states
that the particles in an object vibrate, or move quickly
from side-to-side. The energy of the vibrating particles is
heat. The faster the vibrations, the hotter the object. This
theory explains that warm objects cool down because
they lose energy. The energy moves into the surroundings.
As a result, the particles in the object move more slowly.
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The Nature of Science continued
TESTING SCIENTIFIC THEORIES
Scientific theories are always being questioned and
examined. A theory must continue to pass several tests
in order to be accepted. These tests are shown in the
table below.
Test of Scientific Theories
Example
A theory must clearly explain all
available observations.
The kinetic theory explains why the
hot cooking pot gets cooler when
it is placed on the cooler counter. It
also explains why a hot cup of tea
gets cooler when it is placed in a
cooler room. In fact, it explains why
any hot object cools off in cooler
surroundings.
Experiments that support the theory
must be repeatable.
A hot cooking pot always gets cooler
when placed in cooler surroundings.
No matter how many times you do
this test, the pot will always cool off.
You must be able to predict results
from the theory.
Based on the kinetic theory, you can
predict that any hot object placed in
cool surroundings will cool down.
You can also predict that adding
energy to a cool object will make
the particles in it vibrate faster. This
should cause the object to heat up.
Many experiments have shown that
these predictions are true.
Scientific theories must explain all of the available
information that scientists have. Sometimes, scientists
change or replace theories when new discoveries are
made. For example, more than 200 years ago, scientists
used the caloric theory to explain how objects become
warmer and cooler. This theory stated that heat was an
invisible fluid, called caloric, that flowed from warm
objects to cool ones.
Later, scientists began to realize that caloric theory
could not explain some of their observations. After doing
many experiments, some scientists presented a new theory of heat—the kinetic theory. At first, people criticized
the new theory. However, the kinetic theory was eventually accepted because it explained both old and new
observations.
EHHDBG@<EHL>K
8. Apply Concepts A
scientist adds energy to a
block of metal. According
to the kinetic theory, what
should the scientist predict
will happen to the metal?
READING CHECK
9. Explain Why did scientists
accept the kinetic theory in
place of the caloric theory?
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The Nature of Science continued
How Do Scientists Describe Physical Events?
READING CHECK
10. Define What is a
qualitative statement?
READING CHECK
11. Identify Why do
scientists often use
quantitative statements
instead of qualitative
statements?
READING CHECK
12. Describe Why do
scientists use models?
There are many ways to describe scientific theories
and laws. For example, the law of universal gravitation
describes the gravitational force between two objects.
The law states that gravitational force depends on the
masses of the objects and the distance between them.
This is a qualitative statement of the law of universal
gravitation. Qualitative statements describe processes or
events using words. They are not very precise.
Many times, scientists need to describe things precisely. In those cases, they use quantitative statements.
A quantitative statement is a statement that describes
something precisely. Most quantitative statements use
numbers or equations to describe things.
For example, scientists use an equation to exactly
describe the relationship between mass, distance, and
gravitational force. This equation describes exactly how
large the gravitational force between any two objects will
be. By using this equation, scientists can make quantitative
statements about the effects of gravity.
Qualitative Statement
The gravitational force between two
objects depends on their masses and
on the distance between them.
Quantitative Statement
F=G
m1m2
d2
F is gravitational force, G is a
constant, m1 and m2 are the masses
of the objects, and d is the distance
between the objects.
Scientists may also use models to represent physical
events. A scientific model is something scientists use to
represent an object or event in order to make it easier to
study. In many cases, models represent things that are
too small, too big, or too complex to study easily.
Models can take many forms. Drawings on paper
can be models. Real objects can also be used as models
to help us picture things we cannot see. For example,
a spring can be used as a model of a sound wave. A
model can also be a mental “picture” or set of rules that
describes how something works.
Models have uses in our everyday lives. Computer
models help forecast the weather. For example, scientists
use models like those at the top of the next page to predict
how hurricanes will move.
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The Nature of Science continued
EHHDBG@<EHL>K
13. Explain The model
in the right image is more
accurate than the model
in the left image. How did
scientists make the model
more accurate?
Models like these help scientists predict the paths of hurricanes. By collecting
more data, scientists were able to make the right-hand model more accurate than
the left-hand model.
What Are the Branches of Science?
Scientists study everything from ants and people to
planets and stars. You can think of science as having two
main groups, or branches: social science and natural science. Social science deals with human behavior. Natural
science deals with how “nature,” or the whole universe,
behaves.
Today, natural science has many branches and specialties, as shown in the figure below. The branches of
science sometimes mix. For example, geophysics is the
study of forces that affect Earth. It is both an Earth science and a physical science.
Biological Science:
Science of
living things
Natural
Science
Physical Science:
Science of matter
and energy
14. List What are the two
main branches of science?
Botany
Zoology
Ecology
Many other branches
Physics: forces and energy
Chemistry: matter and its changes
EHHDBG@<EHL>K
Geology
Earth Science:
Science of Earth
READING CHECK
Meteorology
Astronomy
15. Identify Name two
branches of physical science.
Many other branches
The natural sciences include many different types of science.
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Section 1 Review
SECTION VOCABULARY
law a descriptive statement or equation that reliably predicts events under certain conditions
science the knowledge obtained by observing natural events and conditions in order to
discover facts and formulate laws or principles
that can be verified or tested
technology the application of science for practical purposes; the use of tools, machines, materials, and processes to meet human needs
theory a system of ideas that explains many related observations and is supported by a large
body of evidence acquired through scientific
investigation
1. Describe Relationships How are science and technology related?
2. Explain Why did Wilhelm Roentgen repeat his experiment before describing his
results to others?
3. Compare How are scientific theories and laws similar?
4. Describe How is a scientific theory different from a guess or an opinion?
5. Apply Concepts Fill in the blank spaces in the table below.
A scientist who studies…
…works in the branch of…
…how plants and animals interact…
…life science.
…how two chemicals react with each other…
…what causes earthquakes…
…how objects move…
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