DISCOVERY EDUCATION SCIENCE CONNECTION

Aristotle or Ptolemy! The studyof our world must be done withone’s own eyes. In science, theopinion of thousands is not worththe thoughtful reasoning of asingle individual.Pisa, 1590: I have longquestioned Aristotle’s teachingson the motion of falling bodies.Most accept his statement thatthe speed of a falling bodyremains the same throughoutthe fall. This troubles me. Evenmore troubling is the acceptanceof his teaching that the weightof a falling body determines thespeed of its fall.

Following that line of reason,let us suppose that twoobjects—one with a weight of 22 pounds (10 kg),the other 11 pounds (5 kg)—were dropped from the sameheight. According to Aristotle,the heavier object would reachEarth twice as fast as the lighterobject. Though it might seemlogical—and indeed it has beenaccepted for generations—Icannot accept Aristotle’steaching without experiment.For me, a truth cannot bereached unless we measure whatis measurable and makemeasurable what is not.Were it possible, I would presentthe esteemed Greek with thefollowing hypothesis: Suppose Iwere to ascend to the top of the

tower here in Pisa with the twoobjects I previously described.Now suppose I were to connectthe two with a string and dropthe new joined object. Byattaching the lighter, slower-falling weight, would I in factslow the fall of the new object?Or would the linking of the twomake the new object—now 15kilograms in total—fall one andone-half times faster than the10-kilo object and three timesfaster than the 5-kilo object? ForAristotle’s teaching to hold true,the answer to both questionswould have to be yes. Yetcommon sense tells us that theanswer to both questions is no.This division betweenunthinking belief and thoughtfulreason is but one example of thefailure of our society today. Forwho can deny that the worstdisorders occur when we are told

B etween 1589 and 1592, the great scientistGalileo Galilei (1564–

1642) taught geometry andastronomy at the University ofPisa in Italy. During those years,the young teacher also beganwriting a book he titled OnMotion. That book was neverpublished, but many of Galileo’sideas and experiments from thatwork, concerning gravity andfalling bodies, were included inhis later works.

Galileo lived more than acentury before Sir IsaacNewton, the man whodeveloped the laws of motionand gravity. Like Newton,Galileo had beliefs about thenature of the universe that werenot accepted at the time.Throughout his life, Galileomade enemies of people inauthority by questioning theirscientific beliefs—beliefshanded down over the centuriesand accepted without question.For Galileo, any truth had to be proved.

In this historical fiction, thewriter has Galileo pondering therelationship between fallingbodies and gravity. Theitalicized words are directquotes from Galileo.Pisa, 1589: How foolish is themob who blindly follows pastteachings of ancients such as

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to deny our senses and submit toan outside will?Pisa, 1591: My mind has beenconsumed with proving mytheories of falling bodies. Indirect disagreement withAristotle, I contend that whentwo objects of differing weightsare dropped, the lighter objectwill move ahead of the heavierbody in the initial moments ofthe fall. Next, it is my claimthat the speed of a fallingobject increases over the timeof its fall. Further, I contendthat all objects fall at the samespeed, regardless of theirweight, drawn downward bythe force of the ground beneathour feet.Pisa, 1592: Many hours ofwork and thought have helpedto redirect my hypotheses offalling bodies. My studentshave assisted in performing,observing, and measuring myexperiments. From Pisa’sleaning tower, we repeatedlydropped two spheres ofidentical size, one of wood andone of iron. We observed thatindeed the wooden spheresmoved ahead of the iron as thefall began.

As to the other aspectsof my theory, the ironobject did indeedstrike ground beforethe wooden sphere.However, the ironsphere had aweight ten timesgreater than thatof wood. Observers

agreed that the heavier objectdid not fall at a rate ten timesgreater than the lighter object.Though my theory that allobjects fall at the same speedwas not proved, that ofAristotle was disproved. Finally,my third contention involvingthe increase of speed over thetime of a fall was one thatresisted mathematicalmeasurement and thus remainsunproved. Though I have nodoubt of its truth, the laws ofthe universe cannotbe read until theyare written inmathematicallanguage, withoutwhich they areimpossible to comprehend.Florence, 1636: As I completemy latest work, Two NewSciences, I am at last able toadvance my theory of fallingbodies: In a setting without theresistance of air, all bodies fallat the same speed and gainequal amounts of speed during the time of the fall.

DISCOVERY EDUCATION SCIENCE CONNECTION

SPEED CONTROL After his experiments atPisa, Galileo realized that the resistance ofair made it impossible to prove his theorythat all objects fall at the same rate of speed.Now that we have traveled into the airlessand weightless environment of space, histheory has been tested. What variables mustbe controlled when testing gravity’s effect onthe rate of speed of different objects? Designan experiment that controls these variablesand could be implemented on the Moon.