1 The Nature of Science

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1 CHAPTER 1 Introduction to Science 1 The Nature of Science SECTION 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. 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. Scientific Process Investigating Experimenting Observing Confirming results Examples learning about an object or event by watching, measuring, testing, or reading other scientists work setting up a planned, controlled test to find out how something reacts to a change carefully watching, measuring, and writing down information about an object or an event repeating observations and experiments to see whether the results are the same Brainstorm In a small group, talk about ways that you use scientific processes in your everyday life. 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. 1. Identify What are three reasons scientists carry out experiments? Interactive Reader 1 Introduction to Science

2 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. Research Learn more about cathode rays, Roentgen, or another historic scientific discovery. Share what you learn with a partner or a small group. Metal rod Metal rod 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. Interactive Reader 2 Introduction to Science

3 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. 3. Explain Why did Roentgen cover the tube with heavy paper? 4. Describe What made Roentgen think that the tube was producing rays other than cathode rays? 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? Interactive Reader 3 Introduction to Science

4 6. Define What is a scientific law? What Is a Scientific Law? 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. 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. 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. Interactive Reader 4 Introduction to Science

5 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 A theory must clearly explain all available observations. Experiments that support the theory must be repeatable. You must be able to predict results from the theory. Example 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. 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. 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. 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? 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. 9. Explain Why did scientists accept the kinetic theory in place of the caloric theory? Interactive Reader 5 Introduction to Science

6 10. Define What is a qualitative statement? 11. Identify Why do scientists often use quantitative statements instead of qualitative statements? 12. Describe Why do scientists use models? How Do Scientists Describe Physical Events? 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 m m 1 2 d 2 F is gravitational force, G is a constant, m 1 and m 2 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. Interactive Reader 6 Introduction to Science

7 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. 14. List What are the two main branches of science? Biological Science: Science of living things Botany Ecology Zoology Many other branches Natural Science Physical Science: Science of matter and energy Earth Science: Science of Earth Physics: forces and energy Chemistry: matter and its changes Geology Meteorology Astronomy Many other branches 15. Identify Name two branches of physical science. The natural sciences include many different types of science. Interactive Reader 7 Introduction to Science

8 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 how plants and animals interact works in the branch of life science. how two chemicals react with each other what causes earthquakes how objects move Interactive Reader 8 Introduction to Science