Chapter 1: The Nature of Science 5

Science is a process.You can think of science as a continuous process of asking questionsabout the world and seeking answers to those questions. Scientists usemany processes. Typically, scientists studying a topic ask questions,determine what is known about the topic, investigate, interpret theirresults, and share their results. As more knowledge becomes available,scientists also see how this new knowledge affects their ideas. Scientistsare always building on old knowledge and interpreting results in different ways on the basis of new knowledge.

Check Your Reading List five steps that scientists usually take as part of the scientific process.

VOCABULARY

hypothesis p. 6law p. 6

BEFORE, you learned

• Science is a way to explore thenatural world

• Science is based on objectiveobservation

• Scientific ideas can be tested

NOW, you will learn

• What processes scientists use• How scientists use patterns• How scientific ideas change

with time

EXPLORE Assumptions

Can you recognize your assumptions?

PROCEDURE

Use the six toothpicks to make an equilateral triangle, one in which all three sides are the same length.

Now use the same six toothpicks to make two equilateral triangles.

Use the same six toothpicks to make four equilateral triangles.

WHAT DO YOU THINK?• What did you assume, or take for granted, about the

triangles you were forming?• Were you able to do step 3? If not, try to think of more

assumptions you may have unknowingly made. Is there any reason to believe these assumptions are true?

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KEY CONCEPT

Science is an ongoingprocess.

Sunshine StateSTANDARDSSC.H.1.3.1: The studentknows that scientificknowledge is subject tomodification as newinformation challengesprevailing theories andas a new theory leads tolooking at old observa-tions in a new way.SC.H.1.3.2: The studentknows that the studyof the events that ledscientists to discoveriescan provide informa-tion about the inquiryprocess and its effects.SC.H.2.3.1: The studentrecognizes that pat-terns exist within andacross systems.

MATERIALS6 toothpicks

6 Chapter 1: The Nature of Science

Scientists make observations and try to figure out what factorsaffect the things they observe. They try to come up with explanations,or hypotheses, to account for what they notice. A is a tentative explanation for an observation. A hypothesis often explainsthe relationship between two or more different variables. A scientifichypothesis is testable—it leads to a prediction that can be confirmedby new observations.

Scientists look for patterns.When scientists develop hypotheses, they often do so to explain pat-terns that they have noticed. Scientists look for the rules behindpatterns they observe. Patterns come in many forms. A pattern can bea cycle, such as the changing seasons. It can be a relationship, such ashow the volume of a gas changes as the temperature changes. It can bea geometric pattern found in nature, such as the sunflower shown belowon the left that resembles the mathematical pattern on the right.

Patterns can also help scientists understand natural laws and proc-esses. In science, a is a principle or rule that describes a physicalrelationship. Laws always work the same way under the same condi-tions and can be discovered by finding patterns in relationships.

When scientists understand the forms of natural laws and processes,they can then develop hypotheses that explain the patterns they observe.But even if scientists cannot explain why a certain pattern exists, theycan still use the pattern to help them in their investigations.

check your reading How can scientists use patterns?

law

hypothesis

The seeds in this sunflower form a geometricpattern.

This mathematical pattern resembles the naturalpattern in the sunflower.

VOCABULARYMake a description wheelin your notebook for law.

Scientists often discover patterns that can be written down asmathematical formulas. In the early 1600s, German astronomerJohannes Kepler was trying to find a simple way to describe how planets moved. Most scientists of the time thought that the planetsmoved in perfect circles. Kepler had inherited a large amount of dataon the positions of the planets that had been collected by a Danishastronomer named Tycho Brahe (TEE-koh BRAH). Kepler searchedfor circular patterns in the data.

When he found that the data did not fitany circular patterns, he started looking for theactual pattern. He discovered that he could explain the positions of the planets byassuming that the planets orbited the Sun inslightly flattened circles, or ellipses. Kepler alsodiscovered a mathematical relationshipbetween a planet’s distance from the Sun andthe time the planet takes to move around theSun. Kepler’s formulas, however, only describedthe patterns. They did not explain why the patterns existed. That explanation would come later.

Are patterns easy to notice?PROCEDURE

Decide on a simple rule that determines which letter of the alphabet can fol-low another letter in a sequence you are making. For example, your rulemight be that a small letter must follow a capital letter. Write down yourrule, but keep it secret as you follow the next two steps.

Write down a starting letter. Have your partner suggest a letter. If the lettercan come next in your sequence, add it to your sequence.

Have your partner suggest more letters. Each time, place the letter in yoursequence if it follows your rule, or say that it does not fit the rule. Continue until your partner thinks he or she knows the rule.

Now have your partner pick a secret rule, and repeat the procedure. Did each of you figure out the other’s rule?

WHAT DO YOU THINK?Were both rules equally easy to determine?

CHALLENGE How was figuring out your partner’s rule similar to using a prediction to test a hypothesis?

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PatternsPatternsSKILL FOCUSInferring

MATERIALS• pencil• paper

TIME30 minutes

Chapter 1: The Nature of Science 7

Mars693.5 Earth days

Earth365 Earth days

Sun

8 Chapter 1: The Nature of Science

Scientists often build on previous ideas.Scientists do not work in isolation. They are part of a community thatshares its results. Scientists also have access to many ideas that otherscientists have already investigated. They can take an existing hypothesisor theory and extend it to discover something new. They can also usedata that have already been collected and think of new explanationsfor the patterns and rules that others have found.

Sir Isaac Newton, an English scientist and mathematician of thelate 1600s, built his theories on both his own observations and thework of other scientists. It was Newton who provided an explanationfor the laws of planetary motion that Kepler had discovered. Newtonreasoned that a force acted between the Sun and the planets. He alsoreasoned that this was the same force that caused objects to fall toEarth—the force of gravity.

Kepler’s laws enabled Newton to make inferences about the natureof gravity. Newton wondered what properties gravity would have if itwere the force responsible for planetary motion. He determined thatthe force of gravity between two objects must depend upon the massesof both objects and the distance between them. In other words,Newton’s law of gravity explained why the motion of the planetscould be described by Kepler’s formulas.

By studying the work of previous scientists, Newton was able todevelop a set of theories that explained why planets move as they do.Newton acknowledged that he could not have made his discoverieswithout the work of previous scientists. He wrote, “If I have been ableto see further, it was only because I stood on the shoulders of giants.”

The force of gravity between two objects dependson their mass and the distance between them.

Newton’s Law of Gravity

The length of the arrows represents the size of theforce. How do the arrows relate to the captions?

Sir Isaac Newton1642–1727

The greater the masses, the greater the force of gravity.

Objects attract each other because of their masses.

The greater the distance, the smaller the force of gravity.

RESOURCE CENTERCLASSZONE.COM

Learn about anothercase of new informationexpanding and changingold ideas.

reminder

You will learn more aboutgravity in Chapter 4.

Content PreviewFLORIDA

Chapter 1: The Nature of Science 9

Scientific understanding can change withnew information.

As scientists learn more about the universe, the information they collect can challenge existing ideas. Similarly, new ideas can shed lighton existing data. When the data do not agree with a well-establishedand tested theory, scientists usually check both the data and theirassumptions about the theory. Often, it turns out that they did nottake into account some factor when analyzing the data. Sometimes,however, it is the theory that needs to be reconsidered.

Old Ideas and New InformationSometimes new observations do not agree with the predictionsthat can be made based on a hypothesis or theory. Newton’sformulas for gravity and motion allowed scientists to makevery specific predictions about the motions of the planets.For the most part, these predictions proved to be accurate.However, during the mid-1800s, scientists discovered a verysmall difference between Mercury’s predicted motion andits actual motion around the Sun. Because the motions ofthe other planets were so accurately predicted, scientistswere puzzled by Mercury’s motion.

Scientists looked for reasons to explain why Mercury’smotion did not agree with Newton’s theories. One hypothe-sis was that another planet, so close to the Sun that it couldnot be seen, was affecting Mercury’s orbit. But no such planetwas found. Other possible causes were suggested, such as the existence of dust between Mercury and the Sun, but no evidence of these causes was ever found.

check your reading Why did scientists question Newton’s law of gravity?

New Ideas and Old InformationThe mystery of Mercury’s motion was not fully explained until theearly 1900s, when German-born physicist Albert Einstein developed a new way of understanding gravity. Newton had viewed gravity as a force by which objects attract each other because they have mass.Einstein instead thought that perhaps mass distorted space and time.His idea was that an object moving through curved space would also curve.

Mercury, shown here, hadan orbit that could notquite be predicted byNewton’s laws.

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If you roll a marble across a flat rubber sheet that is stretched outlike a trampoline, the marble will travel in a straight line. If you put aheavy weight on the rubber sheet, the sheet will stretch and curve, asshown in the illustration below. If you roll a marble across the sheetnow, its path will be affected by the curve in the sheet. The effect onthe marble is similar to the effect gravity has on moving objects.Einstein used his new ideas about gravity to calculate and predict themotions of the planets. Einstein’s theory accurately predicted the orbitof Mercury. Because Mercury is closer to the Sun than the other plan-ets, the curve of space and time has a more obvious effect on its orbit.Einstein’s formulas predicted this effect accurately.

In Newton’s theory, light could not be affected by gravity. Einstein’stheory, however, predicted that gravity should affect light as well asmatter. In 1919 scientists observed that light was in fact affected bygravity, and Einstein’s ideas became widely accepted.

An object moving through curved space will curve. If gravity isviewed as a curving of space and time, Mercury’s motion can befully explained.

Einstein’s Theory of Gravity

Space with No Mass

If there is no curve to space, anobject moves in a straight line.

Space with Mass

What would a more massive object do to the curve in the rubber sheet?

Mass curves space and time, so a movingobject has a curved path near a mass.

Chapter 1: The Nature of Science 11

Using Old and New IdeasAlthough Einstein’s view of gravity is now accepted asa more complete way to understand gravity, Newton’stheories about gravity are still taught. This is becauseNewton’s formulas are easier to understand and workwith and, in most cases, they predict the correctmotions. Only where gravity is very strong doNewton’s formulas stop giving accurate results. It wasNewton’s formulas, and not Einstein’s, that wereused to send humans to the Moon.

check your reading Why are Newton’s formulas still used today?

Scientists do not usually discard old theoriesthat still work. They are, however, now aware thatthose theories are limited and work only under specific circumstances. But when scientists look at the extreme ends ofthings, new theories are often absolutely necessary. For example, theformulas for motion must be modified for objects traveling close to thespeed of light. Many physical laws must also be modified as scientistsstudy objects as tiny as atoms and molecules.

Scientists are also aware that with new technology and new infor-mation, even topics they thought were very well understood can holdsurprises. Our understanding of gravity may still not be complete.As some of our early spacecraft approach the outer reaches of our solarsystem, their motion is different from what scientists had predicted.While there may be explanations for this that are consistent withNewton’s or Einstein’s theory, some scientists are looking once again atthe current theory of gravity to see if it may need more modification.

KEY CONCEPTS1. What part do hypotheses play

in the scientific process?

2. Why do scientists look for patterns?

3. Explain how a scientific ideacan change with time.

CRITICAL THINKING4. Synthesize Recall when

something you learned about ascientific topic changed theway you thought about it.How did the new informationchange your ideas?

5. Analyze What evidence couldyou use to convince a youngchild that the world is reallyshaped like a ball?

CHALLENGE6. Infer Ella discovered that

1 cm3 of a liquid had a volumeof 2 g. She also found that eachtime she doubled the volume ofthe liquid, the mass also dou-bled. How could Ella expressher findings as a mathematicalformula?

Einstein’s formulas givethe same answers asNewton’s formulas undermost normal conditions.

Albert Einstein 1879–1955