Science Skills 7

1.2 Using a Scientific Approach

Key ConceptsWhat is the goal of ascientific method?

How does a scientific lawdiffer from a scientifictheory?

Why are scientificmodels useful?

Vocabulary◆ scientific method◆ observation◆ hypothesis◆ manipulated

variable◆ responding variable◆ controlled

experiment◆ scientific theory◆ scientific law◆ model

If you’ve ever been caught in the rain without an umbrella, your firstinstinct was probably to start running. After all, the less time you spendin the rain, the less water there is falling down on you. So you mightthink that running in the rain keeps you drier than walking in the rainover a given distance. However, by running in the rain you run intomore raindrops than by walking, thereby wetting more of your face,chest, and legs. Have your instincts been getting you wetter instead ofkeeping you drier?

You now have a question that you can try to answer with a scien-tific approach. Which keeps you drier in the rain—walking or running?

Scientific MethodsIn order to answer questions about the world around them, scientistsneed to gather information. An organized plan for gathering, organ-izing, and communicating information is called a scientific method.Despite the name, a scientific method can be used by anyone, includ-ing yourself. All you need is a reason to use it. The goal of anyscientific method is to solve a problem or to better understand anobserved event.

b. ?

d. ?

a. ?

c. ?

ScientificMethods

Observation

Reading StrategyUsing Prior Knowledge Before you read,copy the web diagram below. Add to theweb diagram what you already know aboutscientific methods. After you read, revise thediagram based on what you have learned.

Figure 6 To run, or not to run: that is the question. Designing Experiments How can you test if running in the rain keeps you drier than walking in the rain over the same distance?

FOCUS

Objectives1.2.1 Describe the steps in a

scientific method.1.2.2 Compare and contrast facts,

scientific theories, and scientificlaws.

1.2.3 Explain the importance ofmodels in science.

1.2.4 Explain the importance ofsafety in science.

Build VocabularyParaphrase Tell students to write thevocabulary terms on a sheet of paperand leave enough space to write thedefinitions. As students read, they shouldwrite the definition in their own words.

Reading Strategya. Forming a hypothesis b. Testing a hypothesis c. Drawing conclusionsd. Developing a theory

INSTRUCT

Scientific MethodsBuild Reading LiteracySequence Refer to page 290D inChapter 10, which provides theguidelines for a sequence.

Figure 7 is a flowchart that shows thesteps of a scientific method. Remindstudents to refer to this figure whenreading about a particular step to helpthemselves understand how that stepfits into the sequence of steps in ascientific method.Visual

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Reading Focus

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Science Skills 7

Print• Reading and Study Workbook With

Math Support, Section 1.2 • Transparencies, Section 1.2

Technology• Interactive Textbook, Section 1.2• Presentation Pro CD-ROM, Section 1.2 • GoOnline, Science News, Nature of science

Section Resources

Section 1.2

Answer to . . .

Figure 6 Possible answer: Take twoidentical pieces of absorbent cloth andmeasure the mass of each. Give thecloths to two people to hold at arm’slength during a rain storm. One personshould walk a fixed distance, and theother should run the same distance.Compare the masses of the wet piecesof cloth.

PPLS

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8 Chapter 1

Figure 7 outlines an example of a scientific method.Each step in the method shown involves specific skills,some of which you will be learning as you read this book.It is important to note that scientific methods can varyfrom case to case. For example, one scientist might followthe steps shown in Figure 7 in a different order, or anothermight choose to skip one or more steps.

Making Observations Scientific investigationsoften begin with observations. An observation is infor-mation that you obtain through your senses. Repeatableobservations are known as facts. For example, when youwalk or run in the rain, you get wet. Standing in the rainleaves you much wetter than walking or running in therain. You might combine these observations into a ques-tion: How does your speed affect how wet you get whenyou are caught in the rain?

Forming a Hypothesis A hypothesis is a proposedanswer to a question. To answer the question raised byyour observations about traveling in the rain, you mightguess that the faster your speed, the drier you will stay inthe rain. What can you do with your hypothesis? For ahypothesis to be useful, it must be testable.

Testing a Hypothesis Scientists perform experiments to testtheir hypotheses. In an experiment, any factor that can change iscalled a variable. Suppose you do an experiment to test if speed affectshow wet you get in the rain. The variables will include your speed,your size, the rate of rainfall, and the amount of water that hits you.

Your hypothesis states that one variable, speed, causes a change inanother variable, the amount of water that hits you. The speed withwhich you walk or run is the manipulated variable, or the variable thatcauses a change in another. The amount of water that you accumulateis the responding variable, or the variable that changes in response tothe manipulated variable. To examine the relationship between amanipulated variable and a responding variable, scientists use con-trolled experiments. A controlled experiment is an experiment inwhich only one variable, the manipulated variable, is deliberatelychanged at a time. While the responding variable is observed forchanges, all other variables are kept constant, or controlled.

What is a hypothesis?

Figure 7 A scientific methodprovides a useful strategy forsolving problems. Inferring Is an observationrequired in order for you toarrive at a question? What doesthis tell you about the strictnessof the scientific method?

Test hypothesiswith furtherexperiments.

Make observation.

Ask question.

Develophypothesis.

Test hypothesiswith an

experiment.

Revisehypothesis.

Analyze dataand draw

conclusions.

Hypothesisis

supported.

Hypothesisis not

supported.

Developtheory.

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Section 1.2 (continued)

Build Science SkillsObserving

Purpose Students observe that as the distance from a light source increases,the brightness decreases.

Materials low-wattage incandescentbulb, power source for the bulb

Class Time 10 minutes

Procedure Darken the room and turnon the bulb. Tell students that its lightcan be considered to be coming from asingle point (a point source). Ask two orthree volunteers to walk around theroom and observe whether the lightfrom the bulb is visible in all parts of theroom. Be sure that volunteers observethe light’s brightness at various distancesfrom the bulb.

Expected Outcome Students will seethat the bulb radiates light in all directionsand that as distance from the bulbincreases, the bulb’s brightness decreases.Kinesthetic, Visual, Group

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Customize for English Language Learners

Increase Word ExposureAsk students who are learning English to makeflashcards for each step of the scientific methodshown in Figure 7. Tell students to write theEnglish words describing the steps on an indexcard. They should also write a brief definition intheir first language on the back of each card.Students can make the flashcards as they read

the section. Then, have students shuffle theircards and place the steps of the scientificmethod in the correct order. Students mayrefer to the definition on the back of the card if they need help. Reinforce that the scientificmethod shown in Figure 7 is only one of manypossible methods.

In 1997, two meteorologists conducted a controlled experiment todetermine if moving faster keeps you drier in the rain. In the experi-ment, both scientists traveled 100 yards by foot in the rain. One of themwalked; the other ran. By measuring the mass of their clothes beforeand after traveling in the rain, the scientists were able to measure howmuch water each had accumulated. One of the controlled variables wassize—the two scientists were about the same height and build. Anotherwas the rate of rainfall—the scientists began traveling at the same timeduring the same rainstorm on the same path. A third was the ability toabsorb water—the scientists wore identical sets of clothes.

Drawing Conclusions The scientists’ rainy-day experimentproduced some convincing data. The clothes of the walking scientistaccumulated 217 grams of water, while the clothes of the running sci-entists accumulated 130 grams of water. Based on their data, thescientists concluded that running in the rain keeps you drier thanwalking—about 40 percent drier, in fact. Now you have scientific evi-dence to support the hypothesis stated earlier.

What happens if the data do not support the hypothesis? In sucha case, a scientist can revise the hypothesis or propose a new one, basedon the data from the experiment. A new experiment must then bedesigned to test the revised or new hypothesis.

Developing a Theory Once a hypothesis has been sup-ported in repeated experiments, scientists can begin to developa theory. A scientific theory is a well-tested explanation for aset of observations or experimental results. For example,according to the kinetic theory of matter, all particles of matterare in constant motion. Kinetic theory explains a wide range ofobservations, such as ice melting or the pressure of a gas.

Theories are never proved. Instead, they become strongerif the facts continue to support them. However, if an existingtheory fails to explain new facts and discoveries, the theory maybe revised or a new theory may replace it.

Scientific LawsAfter repeated observations or experiments, scientists may arriveat a scientific law. A scientific law is a statement that summa-rizes a pattern found in nature. For example, Newton’s law ofgravity describes how two objects attract each other by means ofa gravitational force. This law has been verified over and over.However, scientists have yet to agree on a theory that explainshow gravity works. A scientific law describes an observedpattern in nature without attempting to explain it. The expla-nation of such a pattern is provided by a scientific theory.

Figure 8 An environmentalscientist collects a sample for awater pollution study. Afteranalyzing the sample, the scientistcan draw conclusions about howthe water became polluted.

Science Skills 9

For: Articles on the natureof science

Visit: PHSchool.com

Web Code: cce-0011

Scientific LawsBuild Science SkillsInferring Reinforce the differencebetween a scientific theory and a scientificlaw. Ask, How are scientific lawsaffected by new scientific theories?(Scientific laws aren’t affected because newtheories are new explanations of theobservations. Scientific laws are descriptionsof patterns in nature; they do not explain.Theories are explanations of patternsobserved in nature.) If a scientific lawwere developed in one country, wouldit apply in a different country? Explainyour answer. (Scientific laws applyeverywhere. Scientific laws are different from legal and political laws, which applyonly in specific countries.) Logical

Some students may incorrectly think thatevery hypothesis becomes a theory andthen a law. Help students understand thebasic definitions of these three terms. Forexample, tell students that a hypothesis isa reasonable idea, or reasonable guess,that is often much narrower in scopethan a theory. Explain that some ideas or guesses are incorrect, incomplete, oronly partially correct. Tell students that a theory is an explanation, and help them realize that some explanations areincorrect. When students thoroughlyunderstand the definitions of these threeterms, they will realize that these are notalways part of a progression. Verbal

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Science Skills 9

Answer to . . .

Figure 7 No, an observation is notrequired in order for you to be able topose a question. This tells you that thescientific method should not be thoughtof as a strict sequence of steps, butrather a flexible set of guidelines forinvestigating a problem. The flexibility ofthe scientific method allows for scientiststo be creative in their problem solving.

A proposed answer to a question

Science News provides studentswith current information on articleson the nature of science.

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Scientific ModelsIf you have ever been lost in a city, you know that a street map can helpyou find your location. A street map is a type of model, or representa-tion, of an object or event. Scientific models make it easier tounderstand things that might be too difficult to observe directly. Forexample, to understand how Earth rotates on its axis, you could lookat a globe, which is a small-scale model of Earth. The computer modelin Figure 9 represents the interior of an airplane. Other models helpyou visualize things that are too small to see, such as atoms. As long asa model lets you mentally picture what is supposed to be represented,then the model has done its job.

An example of a mental, rather than physical, model might be thatcomets are like giant snowballs, primarily made of ice. Scientists wouldtest this model through observations, experiments, and calculations.Possibly they would even send a space probe—a visit to a comet reallyis planned! If all of these tests support the idea that comets are made ofice, then the model of icy comets will continue to be believed.

However, if the data show that this model is wrong, then it musteither be changed or be replaced by a new model. If scientists neverchallenged old models, then nothing new would be learned, and wewould still believe what we believed hundreds of years ago. Scienceworks by making mistakes. The fact that newer models are continuallyreplacing old models is a sign that new discoveries are continuallyoccurring. As the knowledge that makes up science keeps changing,scientists develop a better and better understanding of the universe.

What is a model?

Figure 9 Two engineers discussa computer-aided design, or CAD,of an aircraft component.

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Scientific Models

Flaps on an AirplanePurpose Students observe how modelscan be used.

Material sheet of paper

Procedure Tell students that the flapson airplane wings help control how theplane flies. Point out that because youdo not have an airplane in the class, youwill use a model to observe how wingflaps can affect an airplane’s flight. Foldthe sheet of paper into a paper airplane.Throw the plane so the class sees howthe plane flies without flaps. On thetrailing edge of each wing, cut a flap.Bend the flaps into different positionssuch as both up, both down, or one upand one down. Throw the plane withdifferent flap positions and observe howthe plane flies. Ask students if they thinkthe wing flaps on a real airplane wouldhave the same effect.

Expected Outcome Students shouldsee that using the paper airplane as amodel for a real airplane is appropriate.With both flaps down, the planedescends; with both up, it ascends. With one flap up and the other down,the plane turns in the direction of theflap that is up.Visual, Logical

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Section 1.2 (continued)

Section 1.2 Assessment

Reviewing Concepts1. What is the goal of scientific methods?

2. How does a scientific law differ from ascientific theory?

3. Why are scientific models useful?

4. What are three types of variables in acontrolled experiment?

5. Does every scientific method begin with anobservation? Explain.

Critical Thinking6. Classifying The scientists who tested the

hypothesis on running in the rain performedonly one controlled experiment that supportedtheir hypothesis. Can their supportedhypothesis be called a theory? Explain.

7. Designing Experiments Suppose youwanted to find out how running affects yourpulse rate. What would your hypothesis be?Explain how you could test your hypothesis.

8. Using Models A scientific model can takethe form of a physical object or a concept. Listone example of each type of model. Howdoes each one resemble what it is supposedto model?

Working Safely in ScienceScientists working in the field, or in a labora-tory, like those in Figure 10, are trained to usesafe procedures when carrying out investiga-tions. Laboratory work may involve flames orhot plates, electricity, chemicals, hot liquids,sharp instruments, and breakable glassware.

Whenever you work in your science labora-tory, it’s important for you to follow safetyprecautions at all times. Before performing anyactivity in this course, study the rules in theScience Safety section of the Skills Handbook.Before you start any activity, read all the steps.Make sure that you understand the entire pro-cedure, especially any safety precautions thatmust be followed.

The single most important rule for your safety is simple: Alwaysfollow your teacher’s instructions and the textbook directions exactly.If you are in doubt about any step in an activity, always ask yourteacher for an explanation. Because you may be in contact with chem-icals you cannot see, it is essential that you wash your hands thoroughlyafter every scientific activity. Remember, you share responsibility foryour own safety and that of your teacher and classmates.

Science Skills 11

Descriptive Paragraph Write a paragraphdescribing the steps of a scientific method.(Hint: Before you write, use a flowchart toarrange your steps in a particular order.)

Figure 10 Safety plays animportant role in science.Interpreting Photos What safetymeasures are these scientiststaking in their laboratory work?

Working Safely in ScienceUse Visuals

Figure 10 Emphasize that studentsmust study the safety rules before theydo lab activities. Ask, Why are thesescientists wearing goggles? (Becausewhen a liquid is poured or heated, it couldsplash into their eyes.) Visual

ASSESSEvaluate UnderstandingAsk students to name scientific laws. Ifthey name a theory instead of a law,help them understand why what theychose is a theory and not a law.

ReteachUse Figure 7 to review the scientificmethod. Point out that when scientistslearn new information, they may goback to an earlier step in the method.

A scientific method can begin with anobservation that leads to a question and a hypothesized answer. Next, thehypothesis is tested either by makingfurther observations or by performingan experiment. Conclusions are thendrawn from the data.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 1.2.

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Science Skills 11

Answer to . . .

Figure 10 They are wearing goggles,gloves, lab coats, and hair nets.

A representation of anobject or event

4. Three types of variables in a controlledexperiment are manipulated variables,responding variables, and controlled variables.5. No. The order of the steps within ascientific method can vary from case to case.6. Although the data from the meteorologists’experiment supported their hypothesis, thescope of their investigation is too narrow to beconsidered a theory. A scientific theory explainsa broad set of observations and/or supportedhypotheses—not just a single hypothesis.

7. Students will likely hypothesize that runningincreases one’s pulse rate. Students can testtheir hypotheses by performing a controlledexperiment in which the manipulated variableis speed (e.g., running, walking, or standingstill) and the responding variable is pulse rate.8. Possible answer: A globe, a physical model of Earth, has the same shape as Earth. Thequantum mechanical model of the atomdescribes the behavior of electrons around the nucleus.

Section 1.2 Assessment

1. The goal of scientific methods is to solve a problem or to better understand anobserved event.2. A scientific law describes an observedpattern in nature without attempting toexplain it. The explanation of such a patternis provided by a scientific theory.3. Scientific models make it easier tounderstand things that might be too difficultto observe directly.

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Forensic ScienceThe first job of police officers at a crime scene is toseal off the area so that potential evidence is notdisturbed. Such evidence will be sent to a forensicscience laboratory for examination.

Forensic science is the use of scientific methods, such asfingerprint matching or the analysis of clothing fibers, to solvecrimes. As techniques in analytical chemistry have becomemore advanced, the amount of information that can be gleanedfrom tiny crime-scene samples has grown. Forensic science isbecoming ever more powerful as a crime-solving tool.

Criminal investigators need to use several scientific tech-niques. They include making observations, establishing theproblem to be solved, collecting evidence and gatheringinformation, forming hypotheses, analyzing evidence,testing hypotheses, and drawing conclusions.

The crime sceneAt the scene, theinvestigators makeobservations that mayshed light on the natureof the crime. Theinvestigators establishthe problem to besolved—in this case, whocommitted the murder?

DNA evidence canbe obtained from

blood stains.

Collecting evidence and forming a hypothesisForensic scientists take photographs andcollect materials from the crime scene.Investigators use all of the informationgathered to formulate hypothesesabout how and why the crime took place.

12 Chapter 1

Forensic ScienceBackgroundForensic science is any aspect of sciencethat relates to law. It includes methodsfor identifying, collecting, and analyzingevidence that may be related to a crime.At a crime scene, data is often identifiedand collected. Data collection mayinclude taking fingerprints; collectinghair, blood, or tissue samples; or makingplaster casts of tire prints or footprints.Depending on the nature of the crimeand the crime scene, investigators mayalso collect samples of soil, pollen, fibersfrom clothing, or other materials at thecrime scene. In the laboratory,technicians study and analyze thesamples so that they can provideinvestigators with accurate information.Data analysis can shed light on whathappened, where it happened, and evenwho might have committed the crime.

Build Science SkillsAnalyzing Data

Purpose Students compare tire tracks to determine which ones were made bythe same toy car.

Materials modeling clay, at least 5 different toy cars with similar-sizedtires that have different tread, cookingoil, magnifying glass

Class Time 30 minutes

Preparation Flatten a piece of clay foreach group of students. Lightly oil thetread of all the tires on the toy cars.Choose a car and roll the tire across eachpiece of clay to make an impression.

Safety Students who are allergic tocorn or olives should wear plastic glovesand dispose of them carefully.

Procedure Tell students that they areforensic scientists and they must find outwhich car was at the scene of a crimebased on a tire track from the scene. Givestudents a piece of clay with a tire trackand another piece of unmarked clay. Havestudents use the clay to test each car’stires and, as needed, use the magnifyingglass to find a match. Ask each group towrite a short paragraph stating what theydid and why they think they haveidentified the car that made the tracks.

Expected Outcome Students shouldcorrectly identify the car by the similartire patterns. Logical, Visual, Group

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� Describe how criminal investigators usescientific methods to solve their cases. (Hint: start by creating aflowchart of a scientificmethod. Then identify howcriminal investigators carryout each step.)

� Take a Discovery Channel VideoField Trip by watching“Cracking the Case.”

Going Further

Analyzing the evidenceMuch of the physical evidence must beanalyzed in a laboratory. With a bloodsample, for example, DNA is extracted andanalyzed and the blood type is established.

Testing hypotheses against the evidenceInvestigators now test hypotheseson who committed the crime—looking for matches in DNA,fingerprints, or clothingfibers, for example. Insome cases, thistesting excludes asuspect. In othercases it strengthensthe case against aparticular person.

Drawing conclusions To build a convincing caseagainst a suspect, variouspieces and types ofevidence may be needed.Evidence might include afingerprint match, a pieceof clothing left at the crimescene, or a connection tothe murder weapon.

Documents mayprovide evidencefor a motive.

Fibers can link asuspect to acrime scene.

Displacedobjects can helpdetermine asequence ofevents.

Forensic blood sampling Articles froma crime scene, such as the blood-stainedclothing and the hatchet shown here,may match DNA to a suspect.

Science Skills 13

Video Field Trip

Going FurtherA scientific method can include thefollowing steps: observing, posingquestions, formulating a hypothesis,testing the hypothesis, and drawingconclusions. When criminal investiga-tors arrive at a crime scene, they makeobservations and collect evidence. The questions they pose might include,“Who committed the crime?” or “How was the crime committed?”Investigators may then form hypothesesconcerning possible suspects and themethods used to commit the crime. By analyzing the evidence obtained(e.g., fingerprint or DNA analysis), theycan test their hypotheses. The results ofthese analyses may allow investigatorsto draw conclusions about the criminal’sidentity and methodology.Logical

Science Skills 13

Video Field Trip

Cracking the Case

can identify who the fingerprint belongsto? (The tiny imperfections such as ridges thatend abruptly, ridges that split, and ridges thatform little dots; also where these are locatedwith respect to one another) How do detec-tives find fingerprints on an object? (The old method involved spreading powder on thearea. The powder adhered to traces of sweat left behind by contact with the fingers. Thepowder was then lifted off with transparenttape, showing the pattern. Newer methods usefluorescent powder and high intensity lasers to

find prints that could otherwise be missed.)Name two things police detectives andforensic scientists might do to track downthe identity of a car that left a suspicioustire track at a crime scene. (Student answersmay include measure and photograph the area,make a mold of the tire track, and look forirregularities in the mold of the tire tread thatare unique to that tire.)

After students have viewed the Video Field Trip,ask them the following questions: What is themain goal of forensic science? (To analyze cluesto reconstruct past events) What discovery led tothe use of fingerprinting in forensic science?(The discovery that no two people had the samefingerprints) What do forensic scientists lookfor in the pattern of a fingerprint so that they

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