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Enabling JavaScript in your browser will allow you to experience all the features of our site. Learn how to enable JavaScript on your browser. A balanced approach to science in each level Glencoe Science: Level Red is the first book in Glencoe's three-book integrated science series. Level Red provides students with accurate and comprehensive coverage of life, earth, and physical science.

The strong content coverage integrates a wide range of hands-on experiences, critical-thinking opportunities, and real-world applications. See All Customer Reviews. Shop Textbooks. Add to Wishlist. USD Sign in to Purchase Instantly. They also might attend meetings where they make speeches about their work. Like the science-fair student in Figure 13 demon- strates, an important part of doing science is the abil- ity to communicate methods and results to others.

Why do scientists share information? Figure 13 Presentations are one way people in science communicate their findings. How can you tell in which of the years each season had its coldest average? Check your answer: The four coldest seasons were spring , summer , fall , and winter Use your table to find out which season had the greatest difference in temperatures over the three years from through For more practice, visit red.

Rudi Von Briel Different types of questions call for different types of inves- tigations. They wanted to know links to information about the what was inside. To answer their question, building a model— scientific method. Some questions ask about the effects of one factor on ables needed in every experiment another. One way to investigate these kinds of questions is by and summarize the differences doing a controlled experiment. A controlled experiment between them. Variables and Constants Imagine a race in which the lengths of the lanes vary. Some lanes are m long, some are 98 m long, and a few are m long.

When the first runner crosses the finish line, is he or she the fastest? Not necessarily. The lanes in the race have different lengths. Variables are factors that can be changed in an experiment. Reliable experiments, like the race shown in Figure 14, attempt to change one variable and observe the effect of this change on another variable.

The variable that is changed in an experiment is called the independent variable. The dependent variable changes as a result of a change in the independent variable. It usually is the dependent variable that is observed in an experiment. Scientists attempt to keep all other variables constant—or unchanged. Figure 14 The m race is The variables that are not changed in an experiment are an example of a controlled experi- called constants.

Examples of constants in the race include track ment. The distance, track material, material, wind speed, and distance. This way it is easier to deter- and wind speed are constants. The times are varied. Figure 15 Safety is the most important aspect of any investigation. Laboratory Safety In your science class, you will perform many types of inves- tigations. However, performing scientific investigations involves more than just following specific steps. You also must learn how Eye Safety to keep yourself and those around you safe by obeying the safety Clothing Protection symbol warnings, shown in Figure Disposal Biological In a Laboratory When scientists work in a laboratory, as shown in Figure 15, they take many safety precautions.

Extreme Temperature The most important safety advice in a science lab is to think Sharp Object before you act. Always check with your teacher several times in Fume the planning stage of any investigation. Also make sure you know the location of safety equipment in the laboratory room Irritant and how to use this equipment, including the eyewashes, ther- Toxic mal mitts, and fire extinguisher. Animal Safety Good safety habits include the following suggestions.

Before Flammable conducting any investigation, find and follow all safety symbols listed in your investigation. You always should wear an apron and Electrical goggles to protect yourself from chemicals, flames, and pointed Chemical objects. Keep goggles on until activity, cleanup, and handwashing Open Flame are complete. Always slant test tubes away from yourself and oth- ers when heating them. Never eat, drink, or apply makeup in the Handwashing lab. Report all accidents and injuries to your teacher and always wash your hands after working with lab materials.

Figure 16 Safety symbols are present on nearly every investiga- In the Field Investigations also take place outside the lab, in tion you will do this year. List the safety symbols that should streams, farm fields, and other places. Scientists must follow be on the lab the student is prepar- safety regulations there, as well, such as wearing eye goggles and ing to do in Figure Never reach into holes or under rocks. Figure 17 Accidents are not planned. Safety precautions must be followed to prevent injury.

Why have safety rules? Doing science in the class labora- tory or in the field can be much more interesting than reading about it. However, safety rules must be strictly followed, so that the possibility of an accident greatly decreases.

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Think of a person taking a trip in a car. Most of the time when someone drives somewhere in a vehicle, an accident, like the one shown in Figure 17, does not occur. But to be safe, drivers and passengers always should wear safety belts. Likewise, you always should wear and use appropriate safety gear in the lab—whether you are conducting an investigation or just observing. The most important aspect of any investigation is to conduct it safely. Summary Self Check Science Skills 1. Explain the difference between an inference and an. Explain the differences between independent and.

Think Critically A classroom investigation lists bleach Drawing Conclusions as an ingredient. Bleach can irritate your skin, damage your eyes, and stain your clothes. Describe the different types of safety equipment found in a scientific laboratory. Models in Science Why are models necessary? Just as you can take many different paths in an investigation, you can test a hypothesis in many different ways. A model is one way to test a hypothesis.

Models can help you visualize, or picture in your mind, some- Models can be used to help under- thing that is difficult to see or understand. Models can be of things that are too small or too big to see. Models also can show events that and answer questions occur too slowly or too quickly to see. Figure 18 shows different kinds of models. Cell model. Dinosaur model. Types of Models Most models fall into three basic types—physical models, computer models, and idea models. Depending on the reason that a model is needed, scientists can choose to use one or more than one type of model.

Physical Models Models that you can see and touch are called physical models. Examples include things such as a table- top solar system, a globe of Earth, a replica of the inside of a cell, Topic: Topographic Maps or a gumdrop-toothpick model of a chemical compound. They also can be links to information about used to show how things appear when they change position or topographic maps. Activity List some of the differ- ent features found on topographic Computer Models Computer models are built using com- maps and explain their importance when reading and interpreting puter software.

Some computer models can model events that take a long time or take place too quickly to see. For exam- ple, a computer can model the movement of large plates in the Earth and might help predict earthquakes. Computers also can model motions and positions of things that would take hours or days to calculate by hand or even using a calculator.

They can also predict the effect of different systems or forces. Figure 19 shows how computer models are used by scientists to help predict the weather based on the motion of air currents in the atmosphere. What do computer models do? Figure 19 A weather map is a computer model showing weather patterns over large areas.

Scientists can use this information to predict the weather and to alert people to potentially dangerous weather on the way. Figure 20 Models can be cre- ated using various types of tools. Idea Models Some models are ideas or concepts that describe how someone thinks about something in the natural world. Albert Einstein is famous for his theory of relativity, which involves the relationship between matter and energy. This explains that mass, m, can be changed into energy, E. Making Models The process of making a model is something like a sketch artist at work, as shown in Figure The sketch artist attempts to draw a picture from the description given by someone.

The Thinking Like a more detailed the description is, the better the picture will be. Pour 15 mL of water into a vation. Scientific 2. Slowly pour 5 mL of veg- models are made much the same way. The more information a etable oil into the test scientist gathers, the more accurate the model will be. The tube. Add two drops of food col- oring and observe the liq- lived more than 3, years ago, is shown in Figure How are sketches like specific models? Analysis 1. Not all models are for scientific 2. Infer a scientific explana- purposes.

You use models, and you might not realize it. Drawings, maps, recipes, and globes are all examples of models. M Tutankhamun ruled over Egypt. His reign was a short one, and he died when he was just In , his mummified familiar image of the face of King Tut—the gold body was discovered, and in scientists funerary mask that recreated the face of this most famous of was found covering Egyptian kings.

Some of the steps in his skeletal face. Depth markers in red were then glued onto the skull to indicate the likely thickness of mus- cle and other tissue. B Clay was applied to fill in the area between the markers. C Next, the features were sculpted. Here, eyelids are fash- ioned over inlaid prosthetic, or artificial, eyes. Models Communicate Some models are used to communi- cate observations and ideas to other people. Often, it is easier to communicate ideas you have by making a model instead of writ- ing your ideas in words. This way others can visualize them, too.

Models Test Predictions Some models are used to test pre- dictions.


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To test this prediction, the class made a model. Automobile and air- plane engineers use wind tunnels to test predictions about how air will interact with their products. Models Save Time, Money, and Lives Other models are used because working with and testing a model can be safer and less expensive than using the real thing.

For example, the crash- test dummies shown in Figure 22 are used in place of people when testing the effects of automobile crashes. To help train astronaunts in the conditions they will encounter in space, NASA has built a special airplane. This airplane flies in an arc that creates the condition of freefall for 20 to 25 seconds.

Figure 22 Models are a safe and Making several trips in the airplane is easier, safer, and less relatively inexpensive way to test expensive than making a trip into space. Wind tunnels can be used to test new airplane designs or changes made to existing airplanes. Crash-test dummies are used to test vehicles with- out putting people in danger. Astronauts train in a special aircraft that models the conditions of space.

Many years ago, scien- tists thought that Earth was the center An early model of the of the universe and the sky was a blan- solar system had Earth in the center with every- ket that covered the planet. Later, through observation, it was discovered that the objects you see in the sky are the Sun, the Moon, stars, and other planets. This new model explained the solar system differently. Earth was still the center, but everything else orbited it as shown in Figure Models Change Still later, through more observation, it was discovered that the Sun is the center of the solar system.

Earth, along with the other planets, orbits the Sun. In addition, it was discovered that other planets also have moons that orbit them. A new model was developed to show this. Later on, a new model had the Sun Earlier models of the solar system were not meant to be mis- in the center with everything leading. Scientists made the best models they could with the infor- revolving around it.

More importantly, their models gave future scientists information to build upon. Models are not necessarily perfect, but they provide a visual tool to learn from. Summary Self Check Why are models necessary?


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Infer what types of models can be used to model. How are they used to predict weather patterns? Explain how models are used in science. Types of Models 3. Describe how consumer product testing services use mod-. Describe the advantages and limitations of the three Making Models types of models. Think Critically Explain why some models are better than others for certain situations. Give one example. Using Models. Use Proportions On a map of a state, the scale shows that 1 cm is approximately 5 km. If the distance Limitations of Models between two cities is 1. Evaluating Scientific Explanation Believe it or not?

Look at the photo in Figure Do you believe what you see? Do you believe everything you read or hear? What you did was evaluate, or judge the reliability of what you heard. Review Vocabulary prediction: an educated guess as Critical Thinking When you evaluate something, you use to what is going to happen based critical thinking.

Critical thinking means combining what you on observation already know with the new facts that you are given to decide if you should agree with something. You can evaluate an explana- New Vocabulary tion by breaking it down into two parts. Based upon what you know, are the observations accurate? Then you can evaluate the infer- ences—or conclusions made about the observations. Do the conclusions made from the observations make sense? Figure 24 In science, observa- tions and inferences are not always agreed upon by everyone.

Compare Do you see the same things your classmates see in this photo? SuperStock Table 2 Favorite Foods. People's Preference Tally Frequency Pepperoni 37 pizza. Hamburgers 28 with ketchup. Evaluating the Data A scientific investigation always contains observations— often called data. Data are gathered during a scientific investiga- tion and can be recorded in the form of descriptions, tables, graphs, or drawings. When evaluating a scientific claim, you might first look to see whether any data are given. You should be cautious about believing any claim that is not supported by data.

Are the data specific? The data given to back up a claim should be specific. That means they need to be exact. What if your friend tells you that many people like pizza more than Figure 25 These scientists are they like hamburgers? What else do you need to know before writing down their observations you agree with your friend?

You might want to hear about a during their investigation rather specific number of people rather than unspecific words like than waiting until they are back many and more. You might want to know how many people on land. How many people were Draw Conclusions Do you think asked about which kind of food they liked more? When you are this will increase or decrease the given specific data, a statement is more reliable and you are reliability of their data? An example of data in the form of a frequency table is shown in Table 2.

A frequency table shows how many times types of data occur. Scientists must back up their scientific state- ments with specific data. Take Good Notes Scientists must take thor- ough notes at the time of an investigation, as the scientists shown in Figure 25 are doing. Important details can be forgotten if you wait several hours or days before you write down your observations.

Often, great discoveries are made when something unexpected happens in an investigation. You will write down what you do and see during your investigations. Your observations should be detailed enough that another person could read what you wrote and repeat the investigation exactly as you performed it. Practice your observation skills by describing what you see in Figure Can the data be repeated? Scientists also require repeatable evidence.

When a scientist describes an inves- Figure 26 Detailed observations tigation, as shown in Figure 27, other scientists should be able are important in order to get reli- to do the investigation and get the same results. The results must able data. When evaluating scientific data, look to see Observe Use ten descriptive words whether other scientists have repeated the data.

If not, the data to describe what you see happening might not be reliable. Evaluating the Conclusions When you think about a conclusion that someone has made, you can ask yourself two questions. First, does the conclusion make sense? Second, are there any other possible explanations?

Suppose you hear on the radio that your school will be running on a two-hour delay in the morning because of snow. You look outside. The roads are clear of snow. Does the conclusion that snow is the cause for the delay make sense? What else could cause the delay? Maybe it is too foggy or icy for the buses to run. Maybe there is a problem with the school building. The original conclusion is not reliable unless the other possible explanations are proven unlikely. Figure 27 Working together is an important part of science.

Several scientists must repeat an experiment and obtain the same results before data are considered reliable. Evaluating Promotional Materials Scientific processes are not used only in the laboratory. Suppose you saw an adver- tisement in the newspaper like the one in Figure What would you think? You would probably want to hear some of the scientific data supporting the claim before you would believe it. How was this claim tested?

How is the amount of wrinkling in skin measured? You might also want to know if an inde- pendent laboratory repeated the results. An independent laboratory is one that is not related in any way to the company that is selling the product or service. It has nothing Figure 28 All material should to gain from the sales of the product. Results from an independ- be read with an analytical mind. Advertising materials are means. It is important that you carefully evaluate advertising claims and the data that support them before making a quick decision to spend your money. Summary Self Check Believe it or not?

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Describe why it is important that scientific experiments be repeated. List what types of scientific claims should be verified. Think Critically An advertisement on a food package the explanation is based on. Make Evaluating the Data a list of ten questions you would ask when evaluating this claim. Evaluating the Conclusions. Classify Watch three television commercials and read three magazine advertisements. Record the claims that each advertisement made. What is the right answer? Scientists sometimes develop more than one explanation for observations.

Can more than one explanation be correct? Do scientific expla- nations depend on judgment? Real-World Question Can more than one explanation apply to the same observation? Test your model Materials by pulling each of the ropes. Compare your model with those made by others in your class. Procedure 2. Can more than one design give the same result? Can more than one explanation 1.

You will be shown a cardboard tube with apply to the same observation? Your teacher will show you that 3. D—are pulled, the longer rope, B, gets shorter. Pulling on rope B returns the other ropes to their original lengths. Make a display of your working model. Sketch a model of a tube with ropes based Include sketches of your designs. For more on your hypothesis. Using a cardboard tube help, refer to the Science Skill Handbook. In addition to vari- variables, and controls ables and constants, many experi- in the experiment.

A scientist com- draw appropriate con- pares the control trial to the other clusions. What are the various parts of an experiment to test which fertilizer Materials helps a plant grow best? Read the description of the fertilizer experiment. List factors that remained constant in the experiment. Identify any variables in the experiment. Identify the control in the experiment. Identify one possible hypothesis that the gardener could have tested in her investigation. Describe how the gardener went about testing her hypothesis using different types of fertilizers.

Graph the data that the gardener col- lected in a line graph. A gardener was interested in helping her plants grow faster. When she went to the nursery, she found three fertilizers available for her plants. One of those fer- tilizers, fertilizer A, was recommended to her. However, she decided to conduct a test to determine which of the three fer- tilizers, if any, helped her plants grow fastest. The gardener planted four seeds, each in a separate pot. She used the same type of pot and the same type of soil in each pot.

She fertilized one seed. She placed A B C Fertilizer the four pots near one another in her 1 0 0 0 0 garden. She made sure to give each 2 2 4 1 1 plant the same amount of water each day. She measured the height of the 3 5 8 5 4 plants each week and recorded her 4 9 13 8 7 data. After eight weeks of careful 5 14 18 12 10 observation and record keeping, she 6 20 24 15 13 had the following table of data. Analyze Your Data 1. Describe the results indicated by your graph. What part of an investigation have you just done?

Infer Based on the results in the table and your graph, which fertilizer do you think the gardener should use if she wants her plants to grow the fastest? Define Suppose the gardener told a friend who also grows these plants about her results. What is this an example of? Conclude and Apply 1. Would this affect which fertilizer you think the gardener should buy? Why or why not? Explain Does every researcher need the same hypothesis for an experiment?

What is a second possible hypothesis for this experiment different from the one you wrote in step 5 in the Procedure section? Explain if the gardener conducted an adequate test of her hypothesis. Compare your conclusions with those of other students in your class. For more help, refer to the Science Skill Handbook. I s your family doctor Mayer won the Nobel Prize in Physics in a man or a woman?

To your great- Her model greatly increased human grandparents, such a understanding of atoms, which make up question would likely all forms of matter. Growth fac- they are today. But tors regulate the growth of cells and organs that does not in the body. Because of her work, doctors are mean that there better able to understand why tumors form were no female scien- and wounds heal.

Rosalyn Sussman half as exciting Yalow said upon win- as doing the ning the Nobel Prize in work itself. Medicine in for dis- That was the covering a way to measure tiny substances in the fun—seeing it blood, such as hormones and drugs. Maria to diagnose problems that they could not Goeppert detect before. Research Visit the link to the right to research some recent female Nobel prizewinners in physics, chemistry, and medicine. Write a short biography about their lives. How did their discoveries For more information, visit impact their scientific fields or people in general?

What is science? Models in Science 1. Science is a way of learning more about the 1. Models are a graphic representation of an natural world. It can provide possible expla- object or an event used to communicate nations for why and how things happen. Systems are made up of structures, cycles, money, and lives. Evaluating Scientific Science in Action Explanation 1. A hypothesis is a possible explanation based 1. Reliable data are specific and repeatable by on what you know and what you observe. It is important to always follow laboratory 2.

In order for a conclusion to be considered safety symbols and to wear and use appro- reliable, it must make sense and be the priate gear during an experiment. Living systems Earth systems and the ways in which and the systems they interact in space which is the study of which is the study of. Matter and Energy and interactions its ability to of matter change matter.

If the results from your investigation do not support your hypothesis, what should constant p. Earth science p. Which of the following is NOT an exam- ple of a scientific hypothesis? A Earthquakes happen because of stresses Explain the relationship between the words in along continental plates. B Some animals can detect ultrasound 1.

D Lava takes different forms depending 3. Using a computer to make a three- 5. Earth science—physical science dimensional picture of a building is 6. A model C constant 7. Which of the following increases the relia- 9. Which is an example of technology? A a squirt bottle C a cat B a poem D physical science What does it mean to make an inference? A make observations What explains something that takes place B draw a conclusion in the natural world?

An airplane model is an example of what you from splashing acid? Predict the quickest way to get to school in the morning. List some ways you could Draw Conclusions When scientists study how test your prediction. Predict How is using a rock hammer Hypothesize Using a basketball and a ten- an example of nis ball, make a hypothesis about the technology? Drop each ball Compare and Contrast from shoulder height five times, record- How are scientific theories and ing the number of bounces in a table. How are Which ball bounced more? Make a they different? Use the table below to answer question Observe Pour some water in a small dish Hardness and sprinkle some pepper on top.

Notice how the pepper floats on the water. Now Object Mohs Scale add a few drops of liquid soap to the copper 3. Write down your observations as diamond 10 you watch what happens to the pepper. Treasuree Use Tables Mohs hardness scale measures I Island.

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The y Br idg e. Use the table above to identify B which material is the hardest and which is the softest. San Francisco. Give some examples of both types of Use Proportions The map above shows the laws. The scale shows that 1 cm is approximately 1. What is Infer Why it is important to record the approximate distance between Point A and measure data accurately during and Point B?

Record your answers on the answer sheet 5. Which of the following questions can provided by your teacher or on a sheet of paper. What is a rule describing a pattern in A. Why do the leaves on trees change colors nature called? Why do bears hibernate in the winter? Where do waves in the ocean form? What is the most popular book? What is it called when you combine what Use the illustration below to answer questions 2—3.

What are the variables that do not change Mercury in an experiment called? Neptune A. An educated guess based on what you know and what you observe is called which of the following? The model of the solar system best repre- A. Which of the following is not an example of a model? What type of scientist could the person above be classified as? Practice Practice Remember that test taking skills can improve A. If possible, take at least one practice test and B. Earth scientist D.

Record your answers on the answer sheet Record your answers on a sheet of paper. You want to know whether plants grow Use the photo below to answer questions 10 and How would you conduct this experiment? Be sure to identify the independent and dependent variables, and the constants.

Many outdoor clothing products are coated in a special waterproofing agent to protect the material from rain and snow. The manufacturers of the waterproofing agent hire independent field-testers to use their product in the field before marketing it to the public. Why would you want to know the results of the field-testers tests? Use the illustrations below to answer questions 21— Look at the photo above and write down your immediate observations. What safety precautions might this stu- dent want to take?

Explain why science can only provide possi- ble explanations for occurrences in nature. In class it is sometimes not common for students to share their answers on a test. Why is it important for scientists to share What are the above drawings outlining? Body systems interact with one another in Compare and contrast observation and order to function. What would happen if inference. Explain the relationship between science What is the importance of systems in and technology.

What steps do scientists follow when Make a frequency table from the following investigating a problem? Make two observations about the data. List the three branches of science and give lunch; 10 students enjoy peanut butter with examples of questions that they ask. What is the importance of scientific models? The Checkered Flag sections Race car drivers win or lose by tenths of a 1 Description and Measurement second.

The driver has to monitor his fuel usage, speed, and oil temperature in order to 2 SI Units win the race. In this chapter, you will learn Lab Scale Drawing how scientists measure things like distance, 3 Drawings, Tables, and time, volume, and temperature. Graphs Lab Pace Yourself Science Journal As a member of the pit crew, how can you determine the miles per gallon the car uses? Write in Virtual Lab How are graphs used to represent data? Start-Up Activities Measurement Make the fol- lowing Foldable to help you organize information about Measuring Accurately measurements.

You make measurements every day. If you STEP 1 Fold a sheet of paper in want to communicate those measurements half two times length- to others, how can you be sure that they will wise. Unfold understand exactly what you mean? As a class, choose six objects to measure in your classroom. STEP 3 Unfold, lay the paper lengthwise, and 2. Measure each object using the width of draw lines along the folds. Label your your hand and write your measurements table as shown.

Estimate Measure Round 3. Compare your measurements to those of Length It It It. Volume of 4. As you read the chapter, complete the and activities at table. Description and Measurement Measurement How would you describe what you are wearing today? Then you might mention sizes— measurement is by estimating. Measurement is a way to describe the world with num- rounding a number. Measurement can describe the amount of milk in a carton, and accuracy in measurements. It also can describe the volume of water Measurement helps you communi- in a swimming pool, the mass of an atom, or how fast a pen- cate information and ideas.

The circular device in Figure 1 is designed to measure the Review Vocabulary performance of an automobile in a crash test. Engineers use this description: an explanation of an information to design safer vehicles. In scientific endeavors, it is observation important that scientists rely on measurements instead of the New Vocabulary opinions of individuals. Figure 1 This device measures the range of motion of a seat-belted mannequin in a simu- lated accident. Figure 2 Accurate measurement of distance and time is important for competitive sports like track and field.

Describing Events Measurement also can describe events such as the one shown in Figure 2. She ran the race in In this example, measurements convey information about the year of the race, its length, the fin- ishing order, and the time. Information about who competed and in what event are not measurements but help describe the event completely. Estimation can help you make a rect dosage. Any error in dosage or type of pill could rough measurement of an object.

When you estimate, you can harm the patient. Explain use your knowledge of the size of something familiar to estimate how precision and accuracy the size of a new object. If a patient bers are not required. Estimation is a valuable skill that receives the wrong medica- improves with experience, practice, and understanding. Research some other careers that rely on How practical is the skill of estimation?

In many instances, precision and accuracy. A chef makes her prize-winning chili. Figure 3 This student is about 1. Estimate the height of the tree in the photo. Using Estimation You can use comparisons to estimate Measuring measurements. For example, the tree in Figure 3 is too tall to Temperature measure easily, but because you know the height of the student next to the tree, you can estimate the height of the tree.

When Procedure 1. Fill a mL beaker with you estimate, you often use the word about. For example, door- crushed ice. Add enough knobs are about 1 m above the floor, a sack of flour has a mass cold water to fill the of about 2 kg, and you can walk about 5 km in an hour. Estimation also is used to check that an answer is reasonable.

Think about it. Can your friend really run a m dash in 1 s? Record the measurement in your Science Journal. Allow the Precision and Accuracy probe to warm to room One way to evaluate measurements is to determine whether temperature between each they are precise.

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Precision is a description of how close measure- measurement. Suppose you measure the distance 3. Repeat step two using an between your home and your school five times with an odome- alcohol thermometer. Each time, you determine the distance to be 2. Suppose Analysis a friend repeated the measurements and measured 2. Average each set of two days, 2.

Which measuring device is Because your measurements were closer to each other than your more precise? The term preci- you determine which sion also is used when discussing the number of decimal places a is more accurate? A clock with a second hand is considered more precise than one with only an hour hand. Degrees of Precision The timing for Olympic events has become more precise over the years. Events that were measured in tenths of a second years ago are measured to the hun- dredth of a second today.

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Figure 4 shows an example of measurements of time with varying degrees of precision. Accuracy When you compare a measurement to the real, actual, or accepted value, you are describing accuracy. A watch with a second hand is more precise than one with only an hour hand, but if it is not properly set, the readings could be off by an hour or more.

Therefore, the watch is not accurate. However, measurements of 1. Figure 5 illustrates the difference between precision and accuracy. What is the difference between precision and Figure 4 Each of these clocks pro- accuracy? Infer which of the three you could use to be sure to make the bus. Before the invention of clocks, as they are known today, a sundial was used.

As the Sun passes through the sky, a shadow moves around the dial. For centuries, analog clocks—the kind with Digital clocks are now as a face—were the standard. F require precision and accuracy. Archery— a sport that involves shooting arrows into a target—clearly shows the relationship between neither accurate nor precise—the arrows are scattered all around the target. C Here we have a winner! Precision and accuracy are important in many medical procedures.

One of these procedures is the delivery of radiation in the treatment of can- cerous tumors. Because radiation damages cells, it is important Topic: Measurement to limit the radiation to only the cancerous cells that are to be Visit red. A technique called Stereotactic Radiotherapy SRT links to information about the importance of accuracy and allows doctors to be accurate and precise in delivering radiation precision in the medical field.

The patient makes an impression of his or her teeth on a bite plate that is then attached to the radiation Activity Research a topic of interest on the Internet and pres- machine. This same bite plate is used for every treatment to ent the topic and numeric data to position the patient precisely the same way each time. A CAT your class. Rounding a Measurement Not all measurements have to be made with instruments that measure with great precision like the scale in Figure 6. Suppose you need to measure the length of the sidewalk outside your school.

You could measure it to the nearest millimeter. However, you probably would need to know the length only to the nearest meter or tenth of a meter. So, if you found that the length was How would you round this number? To round a given value, follow these steps: 1. Look at the digit to the right of the place being rounded to. The digits to the right of the digit being rounded to are deleted if they are also to the right of a decimal. If they are to the left of a decimal, they are changed to zeros. Look back at the sidewalk example. If you want to round the sidewalk length of Because that digit is a 4, you keep the 8 and round it off to If you want to round to the ones place, you look at the digit to the right of the 5.

In this case you have an 8, so you round up, changing the 5 to a 6, and your answer is m.

Precision and Number of Digits When might you need to round a number? Suppose you want to divide a 2-L bottle of soft drink equally among seven people. When you divide 2 by 7, your calculator display reads as shown in Figure 7. Will you measure exactly 0. All you need to know is that each person gets about 0. Using Precision and Significant Digits The number of digits that truly reflect the precision of a number are called the significant digits or significant figures. The mass of a second object is You need to know these values only to the nearest whole number to solve a problem.

What are the rounded values? This is the procedure you digits 0, 1, 2, 3, 4 remain the same need to use: for digits 5, 6, 7, 8, 9, round up. What are the rounded masses of the objects to the nearest tenth of a unit? Round the following numbers: