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Basic Process SkillsDuring a science course, you often carry out some shortlab activities as well as more detailed experiments. Hereare some skills that you will use as you work.

ObservingIn every science activity, you make a variety of obser-vations. Observing is using one or more of the fivesenses to gather information. Many observationsinvolve the senses of sight, hearing, touch, and smell.

Sometimes you will use tools that increase thepower of your senses or make observations more pre-cise. For example, hand lenses enable you to seethings in greater detail. Tools may help you eliminatepersonal opinions or preferences.

In science it is customary to record your observationsat the time they are made, usually by writing or drawingin a notebook. You may occasionally make records byusing computers, cameras, videotapes, and other tools.As a rule, scientists keep complete accounts of their obser-vations, often using tables to help organize theirobservations in a regular way.

InferringIn science as in everyday life, observations are usuallyfollowed by inferences. Inferring is interpreting anobservation or statement based on prior knowledge.For example, you can make several observations usingthe strobe photograph below. You can observe that the

ball is moving. Based on the motion of the ball, youmight infer that the ball was thrown downward at anangle by an experimenter. In making that inference,you would use your knowledge about the motion ofprojectiles. Someone who knew more about projec-tile motion might infer that the ball loses energy witheach bounce. That is why the height decreases witheach bounce.

Notice that an inference is an act of reasoning, nota fact. That means an inference may be logical but nottrue. It is often necessary to gather further informa-tion before you can be confident that an inference iscorrect. For scientists, that information may comefrom further observations or from research into thework done by others.

PredictingPeople often make predictions, but their statementsabout the future could be either guesses or inferences.In science, a prediction is an inference about a futureevent based on evidence, experience, or knowledge. Forexample, you can say, On the first day next month, it willbe sunny all day. If your statement is based on evidenceof weather patterns in the area, then the prediction isscientific. If the statement was made without consider-ing any evidence, it’s just a guess.

Predictions play a major role in science because theyoffer scientists a way to test ideas. If scientists under-stand an event or the properties of a particular object,they should be able to make accurate predictions aboutthat event or object. Some predictions can be testedsimply by making observations. For others, carefullydesigned experiments are needed.

728 Skills Handbook

Sample Observation Sample Inference

Comparing Observations and Inferences

The ball moves less and less vertical distance in the time between each flash of the strobe light.

Gravity is slowing down the ball‘s upward motion.

The ball moves the same distance to the right in the time between each flash of the strobe light.

Air resistance is so small that it does not slow down the ball‘s horizontal motion.

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MeasuringMeasurements are important in science because theyprovide specific information and help observers avoidbias. Measuring is comparing an object or process to astandard. Scientists use a common set of standards,called the International System of Units, abbreviated asSI (for its French name, Système International d’Unités).

What distance does the ball travel in each timeinterval in the strobe photograph? You can make meas-urements on the photograph to make more precisestatements about the ball’s motion.

CalculatingOnce scientists have made measurements, calculationsare a very important part of analyzing data. How fast isa ball moving? You could directly measure the speed ofa ball using probeware such as a motion sensor. But youcan also calculate the speed using distance and timemeasurements. Calculating is a process in which aperson uses mathematical operations to manipulatenumbers and symbols.

ClassifyingClassifying is grouping items according to some organ-izing idea or system. Classifying occurs in every branchof science but it’s especially important in chemistrybecause there are so many different ways that elementscan combine to form compounds.

Sometimes you place objects into groups using anestablished system. Other times you create a system byobserving a variety of objects and identifying theirproperties. For example, you could group householdcleaners into those that are abrasive and those that arenot. Or you could categorize cleaners as toxic or non-toxic. Ammonia is toxic, whereas vinegar is not.

Using Tables and GraphsScientists represent and organize data in tables andgraphs as part of experiments and other activities.Organizing data in tables and graphs makes it easier tosee patterns in data. Scientists analyze and interpretdata tables and graphs to determine the relationship ofone variable to another and to make predictions basedon the data.

Using ModelsSome cities refuse to approve new tall buildings if theywould cast shadows on existing parks. As architectsplan buildings in such locations, they use models toshow where a proposed building’s shadow will fall atany time of day at any season of the year. A model is amental or physical representation of an object, process,or event. In science, models are usually made to helppeople understand natural objects and the processesthat affect these objects.

Models can be varied. Mental models, such as math-ematical equations, can represent some kinds of ideasor processes. For example, the equation for the surfacearea of a sphere can model the surface of Earth,enabling scientists to determine its size. Models can betwo-dimensional (flat) or three-dimensional (havingdepth). In chemistry, for example, there are several waysto model the arrangement of atoms in a molecule. Twomodels for a water molecule are shown above. The elec-tron dot model is two-dimensional. It has theadvantage of clearly showing how electrons are sharedamong atoms in the molecule. The space-filling modelcannot show the number of electrons inside the atomsor between atoms, but it does show the arrangement ofatoms in space.

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Experimental MethodsA science experiment is a procedure designed so thatthere is only one logical explanation for the results.Some types of experiments are fairly simple to design.Others may require ingenious problem solving.

Posing Questions As a gardener harvested corn in her vegetable garden,she noticed that on one side of the garden the plantsproduced very few ears of corn. The gardener won-dered, Why didn’t the plants on one side of the gardenproduce as much corn?

An experiment may begin when someone like thegardener asks a specific question or wants to solve aparticular problem. Sometimes the original questionleads directly to an experiment, but often researchersneed to restate the problem before they can design anappropriate experiment. The gardener’s question aboutthe corn, for example, is too broad to be tested by anexperiment, since there are so many possible differentanswers. To narrow the topic, the gardener might thinkabout several related questions: Were the seeds the sameon both sides of the garden? Was the sunlight the same? Isthere something different about the soil?

Formulating HypothesesIn science, a question about an event is answered bydeveloping a possible explanation called a hypothesis.The hypothesis may be developed after long thought andresearch or come to a scientist “in a flash.” To be useful, ahypothesis must lead to predictions that can be tested.

In this case, the gardener decided to focus on thequality of the soil on each side of her garden. She didsome tests and discovered that the soil had a lower pHon the side where the plants did not produce well. Thatled her to propose this hypothesis: If the pH of the soilis too low, the plants will produce less corn. The next stepis to make a prediction based on the hypothesis, forexample, If the pH of the soil is increased using lime, theplants will yield more corn. Notice that the predictionsuggests the basic idea for an experiment.

Designing ExperimentsA carefully designed experiment can test a predictionin a reliable way, ruling out other possible explanations.As scientists plan their experimental procedures, theypay particular attention to the variables that must becontrolled and the procedures that must be defined.

The gardener decided to study three groups of plants:Group 1—20 plants on the side of the garden with a

low pH;Group 2—20 plants on the side of the garden with a

low pH, but with lime added; andGroup 3—20 plants on the side of the garden with a

high pH.

Controlling VariablesAs researchers design an experiment, they identify thevariables, factors that can change. Some common vari-ables include mass, volume, time, temperature, light,and the presence or absence of specific materials. Anexperiment involves three categories of variables. Thefactor that scientists purposely change is called themanipulated variable. The factor that may changebecause of the manipulated variable and that scientistswant to observe is called the responding variable. Andthe factors that scientists purposely keep the same arecalled the controlled variables. Controlling variableshelps make researchers confident that the observedchanges in the responding variable are due to changesin the manipulated variable.

For the gardener, the manipulated variable is the pHof the soil. The responding variable is the number ofears of corn produced by the plants. Among the vari-ables that must be controlled are the amount ofsunlight received each day, the time of year when seedsare planted, and the amount of water the plants receive.

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Forming Operational DefinitionsIn an experiment, it is often necessary to define one ormore variables explicitly so that any researcher couldmeasure or control the variable in exactly the same way.An operational definition describes how a particularvariable is to be measured or how a term is to be defined.In this context, the term operational means “describingwhat to do.”

The gardener, for example, has to decide exactlyhow much lime to add to the soil. Can lime be addedafter the seeds are planted or only before planting? Atwhat pH should no more lime be added to the soil? Inthis case, the gardener decided to add lime only beforeplanting, and to add enough lime to make the pH equalin Groups 2 and 3.

Analyzing DataThe observations and measurements that are made inan experiment are called data. Scientists customarilyrecord data in an orderly way. When an experiment isdone, the researcher analyzes the data for trends or pat-terns, often by doing calculations or making graphs, todetermine whether the results support the hypothesis.

For example, the gardener regularly measured andrecorded data such as the soil moisture, daily sunlight,and pH of the soil. She found that the soil pH inGroups 2 and 3 started the same, but after two monthsthe soil pH for Group 3 was a little higher than the soilpH for Group 2.

After harvesting the corn, the gardener recorded thenumbers of ears of corn produced by each plant. Shetotaled the number of ears for each group. Her resultswere the following.

Group 1: 67 ears of cornGroup 2: 102 ears of cornGroup 3: 126 ears of corn

The overall trend was clear: The gardener’s predictionwas correct.

Drawing ConclusionsBased on whether the results confirm or refute thehypothesis, researchers make a final statement thatsummarizes the experiment. That final statement iscalled the conclusion. For example, the gardener’s con-clusion was, Adding lime to soil with a low pH willimprove the production of corn plants.

Communicating ResultsWhen an experiment has been completed, one or moreevents may follow. Researchers may repeat the experi-ment to verify the results. They may publish theexperiment so that others can evaluate and replicatetheir procedures. They may compare their conclusionwith the discoveries made by other scientists. And theymay raise new questions that lead to new experiments.For example, Why does the pH level decrease over timewhen soil is treated with lime?

Evaluating and RevisingScientists must be flexibleabout the conclusions drawnfrom an experiment. Furtherresearch may help confirmthe results of the experimentor make it necessary to revisethe initial conclusions. Forexample, a new experimentmay show that lime can beeffective only when certainmicrobes are present in thesoil. Scientists continuouslyevaluate and revise experi-ments based on the findingsin new research.

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What Is a “Control Group”?When you read about certain experiments, youmay come across references to a control group(or “a control”) and the experimental groups. Allof the groups in an experiment are treatedexactly the same except for the manipulatedvariable. In an experimental group, themanipulated variable is being changed. Thecontrol group is used as a standard ofcomparison. It may consist of objects that are notchanged in any way or objects that are beingtreated in the usual way. For example, in thegardener’s experiment, Group 1 is the controlgroup, because for these plants nothing is doneto change the low pH of the soil.

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