"Annenberg Media" "¶" "CAPTIONING IS MADE POSSIBLE BY THE ANNENBERG/CPB PROJECT" "OSCILLATIONSCANTRAVEL THROUGHA MEDIUM" "SUCHASAIRORWATER" "WITHOUTCARRYINGMATTER ALONGWITHTHEM." "THESE MECHANICAL DISTURBANCES ARECALLEDWAVES." "IN ANY ERA," "THERE ARE CERTAIN EXPERIMENTS WHICH ARE JUST BARELY POSSIBLE." "THESE ARE EXPERIMENTS AT THE STATE OF THE ART." "THEY'RE A TEST OF THE SKILL AND INGENUITY" "OF THE FINEST EXPERIMENTAL PHYSICISTS." "AN EXAMPLE TODAY MIGHT BE" "THE ATTEMPT TO DETECT GRAVITY WAVES" "COMING FROM DISTANT STARS." "IN THE LATE 1600s, A STATE-OF-THE-ART EXPERIMENT" "WAS TO MEASURE THE SPEED OF SOUND." "SOUND NORMALLY COMES TO US THROUGH THE AIR." "IF THERE WERE NO AIR HERE, YOU WOULDN'T HEAR ME SPEAKING." "OF COURSE, YOU WOULD HAVE MORE SERIOUS PROBLEMS." "SOUND TRAVELS VERY FAST," "BUT ITS SPEED IS NOT INFINITE." "WE CAN HEAR ECHOES," "SOUND REFLECTING FROM DISTANT WALLS." "WE SEE LIGHTNING BEFORE WE HEAR THUNDER" "BECAUSE LIGHT TRAVELS MUCH FASTER THAN SOUND." "300 YEARS AGO," "ONE OF THOSE WHO TRIED TO MEASURE THE SPEED OF SOUND" "WAS ISAAC NEWTON HIMSELF." "HIS MEASUREMENT WAS NOT THE BEST IN HIS ERA." "EXPERIMENTAL PHYSICS WAS NOT NEWTON'S STRONG POINT." "BUT IT'S INTERESTING TO SEE" "HOW HE TRIED TO MAKE THE MEASUREMENT." "AT TRINITY COLLEGE," "THERE WAS A CORRIDOR WITH AN ECHO." "HE TRIED TO MEASURE THE TIME A SOUND TOOK" "TO GET DOWN THE CORRIDOR AND RETURN." "AS A TIMING DEVICE, HE USED A SIMPLE PENDULUM." "THE TIME A PENDULUM TAKES TO MAKE ONE FULL SWING" "DEPENDS ON ITS LENGTH." "AS A SHARP NOISE WENT OFF, THE PENDULUM WAS RELEASED." "IF THE PENDULUM RETURNED BEFORE THE SOUND," "THE PENDULUM WAS MADE LONGER." "IF THE SOUND RETURNED FIRST," "THE PENDULUM WAS MADE SHORTER." "THAT WAY, HE COULD GET CLOSER AND CLOSER" "TO THE EXACT AMOUNT OF TIME IT TOOK THE SOUND" "TO GO DOWN THE CORRIDOR AND COME BACK," "AND THEREBY MEASURE THE SPEED OF SOUND." "SOUND IS A WAVE," "A DISTURBANCE THAT TRAVELS AT A DEFINITE SPEED," "LIKE THE WAVES IN THIS MACHINE." "A GOOD POINT TO START OUR DISCUSSION OF WAVES" "IS WITH TWO HARMONIC OSCILLATORS LIKE THESE," "WHICH ARE COUPLED TOGETHER." "WATER," "LIGHT," "SOUND," "EVEN PRESSURE" "THEY ALL TRAVEL IN WAVES." "IN FACT, THROUGHOUT THE PHYSICAL WORLD," "WAVES ARE ONE OF THE MOST COMMON NATURAL PHENOMENA." "AND NATURE ISN'T THE ONLY ONE WHO CAN MAKE WAVES." "PEOPLE CAN MAKE WAVES OF THEIR OWN." "THEY'VE BEEN DOING IT FOR A VERY LONG TIME." "NEW YORK CITY, 1926." "A BIG WELCOME FOR GERTRUDE EDERLE," "THE FIRST WOMAN TO SWIM THE ENGLISH CHANNEL." "THERE'S MORE GOING ON HERE THAN MEETS THE EYE." "THIS IS A HUMAN SHOCK WAVE," "WITH A CIRCULAR WAVE FRONT" "LIKE THE MOLECULAR MOTIONS OF A SOUND WAVE IN A GAS." "THE WAVE MOVES FROM PERSON TO PERSON," "LEAVING A PARTIAL VACUUM IN ITS WAKE." "THIS NONRECURRENT WAVE FRONT WAS HARMLESS." "THIS ONE WAS NOT." "ENIWETOK, 1952." "THE FIRST HYDROGEN BOMB TEST." "THE WORLD AT LARGE FEELS THE HEAT" "OF THE FIRST NUCLEAR SHOCK WAVE IN THE COLD WAR." "BUT THE PHENOMENON OF SPREADING WAVES" "GOES BACK CONSIDERABLY FARTHER THAN 1952," "MUCH FARTHER BACK THAN 1926." "IT GOES BACK TO THE VERY BEGINNING OF TIME" "AND THE UNIVERSE ITSELF, IN FACT." "THE BIG BANG." "AND FROM THE VERY BEGINNING OF IT ALL," "A DISTURBANCE IN ONE PLACE, NATURAL OR OTHERWISE," "INEVITABLY CAUSES A REACTION IN ANOTHER." "AND SO IT GOES." "DISTURBED WEATHER IN A POLAR REGION CAUSES TROUBLE" "ON A TROPICAL ISLE HALFWAY AROUND THE GLOBE." "[THUNDER]" "THE CHAIN OF EARTHLY EVENTS AND PHENOMENON," "WHICH ARE HOOKED TOGETHER BY INFINITELY COMPLEX LINKS," "IS OFTEN BETTER SEEN AT A DISTANCE." "BUT IT CAN BE BETTER UNDERSTOOD CLOSE UP." "THAT'S BECAUSE NO MATTER HOW COMPLEX THE SYSTEM APPEARS," "AN UNDERLYING PRINCIPLE" "BEGINS TO EXPLAIN ITS PHYSICAL ASPECTS." "WHEN SIMPLE MECHANICAL SYSTEMS ARE JOINED," "A DISTURBANCE IN ONE WILL PASS ON TO THE NEXT." "WHEN ANY STABLE MECHANICAL SYSTEM IS DISTURBED," "NATURE'S RESPONSE IS SIMPLE HARMONIC MOTION." "FOR A SINGLE OSCILLATOR, THAT'S AS FAR AS IT GOES." "BUT WHEN OSCILLATORS ARE LINKED" "FROM ONE TO THE NEXT AND TO THE NEXT," "A DISTURBANCE IN ONE PASSES ON TO THE NEXT" "AND CONTINUES ON DOWN THE LINE." "THIS IS THE ESSENCE OF A MECHANICAL WAVE." "SOMETIMES, INDIVIDUAL MECHANICAL OSCILLATORS" "ARE EASY TO DISCERN." "IN OTHER CASES," "THE WAVE ITSELF IS EASIER TO SEE THAN THE INDIVIDUAL OSCILLATORS." "PERHAPS MORE SURPRISING," "WAVES PROPAGATE NOT ONLY ALONG THE SURFACE OF WATER," "BUT EVEN THROUGH THE INTERIOR OF A CRYSTALLINE SOLID." "A DISTURBANCE'S SPEED" "DEPENDS ON THE MEDIUM THROUGH WHICH IT PASSES" "AND ON THE CONNECTION" "BETWEEN ONE BIT OF MATTER AND THE NEXT." "IF THE LINKAGE IS WEAK, THE DISTURBANCE PASSES SLOWLY." "IF IT'S STRONG, THE DISTURBANCE TRAVELS RAPIDLY." "BUT NO MATTER THE SPEED OR THE MEDIUM" "WATER, AIR, OR EVEN A SOLID" "ALL WAVES THAT PROPAGATE THROUGH ANY MEDIUM" "ARE CALLED MECHANICAL WAVES." "MECHANICAL WAVES, OR IMPULSES," "PASS THROUGH A CRYSTAL FROM ATOM TO ATOM" "BECAUSE EACH ATOM IS BOUND TO AN EQUILIBRIUM POSITION" "BY ELECTRICAL FORCES." "WHEN DISTURBED, THEY ACT MECHANICALLY," "EXACTLY LIKE MASSES CONNECTED BY SPRINGS." "WHEN AN IMPULSE MOVES THROUGH A SYSTEM," "NO SINGLE OSCILLATOR GOES VERY FAR," "BUT THE DISTURBANCE MOVES RIGHT ALONG." "[ORCHESTRA PLAYS]" "SOMETIMES, MECHANICAL OSCILLATIONS" "CAN BE MORE MOVING THAN DISTURBING..." "CAN BE ART AS WELL AS SCIENCE," "AND IT CAN BE ENJOYED AS BOTH." "MUSICAL INSTRUMENTS SEND CONTINUOUS WAVES" "THROUGH THE AIR" "THAT CAN BE VISUALIZED AS WELL AS HEARD." "MASSES CONNECTED BY SPRINGS" "MAY NOT LOOK LIKE BEAUTIFUL MUSIC," "BUT THE PRINCIPLE IS THE SAME." "IT CAN BE DESCRIBED USING A FEW TERMS." "EACH WAVE HAS AN AMPLITUDE, THE SIZE OF THE DISTURBANCE," "WHICH IS PRESERVED AS THE WAVE MOVES ALONG." "IT ALSO HAS A DEFINITE TIME FOR EACH COMPLETE CYCLE," "CALLED THE PERIOD." "THE INVERSE OF THE PERIOD IS CALLED THE FREQUENCY." "THE TONE OF MUSIC DEPENDS ON ITS FREQUENCY." "THE HIGHER THE FREQUENCY," "THE HIGHER THE TONE OR PITCH OF THE SOUND." "AND THE LOUDNESS OF MUSIC DEPENDS ON THE AMPLITUDE." "BUT NO MATTER HOW LOUD," "SOUNDS ARE ALWAYS ON THE MOVE." "AND REGARDLESS OF PITCH OR LOUDNESS," "ALL SOUND TRAVELS THROUGH THE AIR" "AT EXACTLY THE SAME SPEED." "IF IT DIDN'T," "EVERY LISTENER WOULD HEAR A DIFFERENT PERFORMANCE." "WHETHER IT'S SHORT AND SWEET OR LOUD AND LONG," "EVERY WAVE HAS A DEFINITE DISTANCE" "FROM ONE COMPRESSION TO THE NEXT" "CALLED THE WAVELENGTH." "THE WAVELENGTH = THE PERIOD" "TIMES THE SPEED OF THE WAVE." "OR, IN OTHER WORDS," "FREQUENCY TIMES WAVELENGTH = SPEED." "LOWER FREQUENCY GENERATES A LONGER WAVELENGTH," "BUT THE SPEED REMAINS THE SAME." "FOR SOUND WAVES IN AIR," "THE SPEED IS ALWAYS THE SAME," "REGARDLESS OF THE FREQUENCY, THE WAVELENGTH," "OR EVEN THE AMPLITUDE." "BUT IN THIS WORLD," "ALL WAVES DON'T GET AN EVEN BREAK." "SOUND AND WATER WAVES TRAVEL AT DIFFERENT SPEEDS." "AND UNLIKE SOUND WAVES, WATER WAVES CAN TRAVEL" "AT SPEEDS DIFFERENT FROM EACH OTHER." "FAR AWAY FROM A CONTINENT," "WAY OUT THERE IN THE SEA," "LONG WAVES TRAVEL FASTER THAN SHORT ONES." "BUT CLOSER TO THE SHORE, WAVES TRAVEL TOGETHER." "AND NO MATTER THEIR LENGTH," "ALL WAVES DECREASE IN SPEED" "AS THEY APPROACH THE SHORE." "IN THE MECHANICS OF WAVES," "THAT'S THE LONG AND THE SHORT OF IT." "BECAUSE ON LAND OR AT SEA" "IN FACT, ANYWHERE AT ALL" "ALL MECHANICAL WAVES FOLLOW THE SAME BASIC PRINCIPLES." "WHEREVER ANYTHING MAKES WAVES, HARMONIC OSCILLATORS RESPOND" "AND THEN SPRING BACK." "THE OSCILLATORS ARE LINKED IN SUCH A WAY" "THAT EVERY CYCLE OF ONE" "EXCITES THE OSCILLATOR BESIDE IT." "BUT WHAT DETERMINES HOW FAST THE WAVE MOVES?" "FORMASSES CONNECTEDBYSPRINGS," "THESPEEDOF THEWAVE" "DEPENDSONTHESTIFFNESS OFTHESPRING," "THE MASS OF EACH OSCILLATOR," "AND THE EQUILIBRIUM DISTANCE BETWEENTHEM." "INWATER, GRAVITYISTHEFORCE" "THATMAKESTHEWATER SPRINGBACK." "THAT'SWHYGRAVITY DETERMINESTHESPEED" "ATWHICH AWATERWAVETRAVELS." "SODOESTHELENGTH OFTHEWAVEITSELF." "IF THE WATER IS MUCH DEEPER THANTHEWAVELENGTH," "THEWAVESPEED ISAPPROXIMATELYEQUALTO" "THESQUAREROOTOFg , THE ACCELERATION OF GRAVITY," "TIMESTHEWAVELENGTH, DIVIDEDBY2PI." "IN OTHER WORDS, LONG OCEAN WAVES MOVE RAPIDLY," "WHILE SHORT RIPPLES MOVE MORE SLOWLY." "THE RESULT IS THAT IN DEEP WATER," "LONG WAVES PASS RIGHT UNDER THE SURFACE RIPPLES." "AND WHETHER THEY'RE LONG WAVES OR RIPPLES," "WATER WAVES DIFFER FROM SIMPLE MECHANICAL ONES" "IN SOME OTHER WAYS." "FOR EXAMPLE, MASSES AND SPRINGS CAN OSCILLATE" "ALONG THE DIRECTION THAT CONNECTS THEM." "THESE ARE CALLED LONGITUDINAL WAVES." "AND THEY CAN ALSO BE MADE TO WAVE SIDEWAYS." "THESE ARE CALLED TRANSVERSE WAVES." "BUT WATER WAVES ARE NEITHER LONGITUDINAL NOR TRANSVERSE." "INSTEAD, EACH BIT OF WATER ON THE SURFACE" "MOVES AROUND IN A LITTLE CIRCLE," "EACH CIRCLE SLIGHTLY OFFSET FROM THE NEXT," "ALTOGETHER, GIVING THE FAMILIAR UNDULATION" "OF THE WATERY SURFACE." "AS A WATER WAVE APPROACHES THE SHORE," "IT COMES INTO EVER-INCREASING CONTACT WITH THE SEABED," "WHICH SLOWS IT DOWN." "THE CLOSER THE SURFACE IS TO THE BOTTOM," "THE SLOWER THE WAVE." "IN SHALLOW WATER," "THE WAVE SPEED IS APPROXIMATELY EQUAL TO" "TO THE SQUARE ROOT OF THE ACCELERATION OF GRAVITY" "TIMES THE DEPTH OF THE WATER." "WHEN THIS HAPPENS, THE THICK PART OF THE WAVE" "MOVES FASTER THAN THE THIN PART," "SPOILING ITS SINE-WAVE FORM," "AND ULTIMATELY CAUSING THE WAVE TO BREAK." "SOUND WAVES CAN BE HEARD BUT NOT SEEN." "WAVES OF SOUND ARE GENERATED" "BY SOMETHING VIBRATING THE AIR." "A VIBRATING OBJECT" "SETS THE AIR NEXT TO IT INTO MOTION," "COMPRESSING AND EXPANDING ITS DENSITY" "WITH EACH VIBRATION." "A GENERATED SOUND WAVE" "CARRIES THE SAME FREQUENCY AS ITS SOURCE." "THE FORCE THAT DRIVES A SOUND WAVE" "COMES FROM PRESSURE CHANGE" "AS AIR DENSITY INCREASES OR DECREASES." "JUSTASTHESPEED OFWATERWAVES" "DEPENDSONGRAVITY," "THESPEEDOF SOUND DEPENDSON" "THEPRESSURE ANDDENSITYOF AIR." "INAIR,THESPEEDOFSOUND  ISAPPROXIMATELYEQUALTO" "THESQUAREROOT OFTHEPRESSURE" "DIVIDEDBYTHEDENSITY OFTHEAIR." "AROUND THE WORLD, IN THE MOST GENTLE SETTING," "OR THE MOST VIOLENT," "COUNTLESS BITS OF MATTER VIBRATE IN UNISON." "AND ACCORDING TO THE PRINCIPLES OF HARMONIC MOTION," "THEY CREATE THE PHENOMENON OF THE MECHANICAL WAVE." "NOW, WE UNDERSTAND WHY ISAAC NEWTON" "WAS PLAYING WITH A PENDULUM" "IN A CORRIDOR AT TRINITY COLLEGE." "HE HAD A THEORY OF THE SPEED OF SOUND" "AND DECIDED IT SHOULD EQUAL" "THE SQUARE ROOT OF THE ATMOSPHERIC PRESSURE" "DIVIDED BY AIR DENSITY." "WHEN HE PUT IN THOSE VALUES" "TO FIND OUT HOW BIG IT SHOULD BE," "THE RESULT WAS 979 ENGLISH FEET PER SECOND." "NEWTON WAS TRYING TO MEASURE THE SPEED" "IN ORDER TO SEE IF HIS THEORY WAS RIGHT." "NOW, NEWTON'S MEASUREMENT WAS NOT THE VERY BEST." "THE BEST OF THAT TIME WAS MADE BY WILLIAM DERHAM" "WHO GOT A RESULT OF 1,142 FEET PER SECOND." "AT THIS POINT, NEWTON HAD TO DO" "WHAT EVERY SCIENTIST MUST DO." "HE HAD TO MAKE A VALUE JUDGMENT." "HIS THEORY PREDICTED THIS NUMBER." "THE EXPERIMENT MEASURED THIS RESULT." "THE QUESTION IS, "IS THAT GOOD OR BAD?" ""IS THE AGREEMENT OR DISAGREEMENT" "BETWEEN THESE NUMBERS SATISFACTORY OR UNSATISFACTORY?"" "WE KNOW IN RETROSPECT, THAT WHAT NEWTON HAD DONE" "WAS AN ABSOLUTELY STUNNING INTELLECTUAL ACCOMPLISHMENT." "BEFORE NEWTON, NOBODY HAD THE FOGGIEST NOTION" "OF WHAT THE SPEED OF SOUND SHOULD BE." "NEWTON CAME ALONG," "HAD THE RIGHT IDEA OF WHAT SOUND WAS," "AND CALCULATED A SPEED THAT WAS CORRECT TO WITHIN 20%." "SO HE SHOULD HAVE BEEN SATISFIED." "NEWTON CONSIDERED THIS SITUATION," "AND HE FOUND IT TOTALLY, COMPLETELY, UNACCEPTABLE" "BECAUSE THE ENTIRE THRUST OF THE SCIENTIFIC REVOLUTION" "FROM THE TIME OF COPERNICUS ON," "WAS TO CAST MAGIC AND THE OCCULT OUT OF SCIENCE." "NEWTON HAD INTRODUCED HIS THEORY OF GRAVITATION" "IN WHICH INVISIBLE FORCES ACTED BETWEEN BODIES" "AT VAST DISTANCES WITH NOTHING IN BETWEEN." "THAT SMELLED TO NEWTON AND HIS CONTEMPORARIES" "LIKE MAGIC." "NEWTON'S DEFENSE OF HIS THEORY WAS" "THAT IT WAS RIGHT BECAUSE IT WORKED." "IT GAVE PRECISELY CORRECT NUMERICAL PREDICTIONS." "THAT IS THE TRUE TEST" "OF THE CORRECTNESS OF A SCIENTIFIC IDEA." "IF PRECISE AGREEMENT IS THE TRUE TEST" "OF HIS THEORY OF GRAVITY," "IT HAD TO BE THE TRUE TEST" "OF HIS THEORY OF THE SPEED OF SOUND" "WHICH WAS WRONG BY 20%." "NEWTON SET OUT TO MAKE HIS THEORY CORRECT." "WHAT HE DID HAS A SPECIAL NAME." "IT'S CALLED FUDGING." "NO SCIENTIST EVER DOES IT." "AND THIS IS FUDGING BY THE GREAT SIR ISAAC NEWTON" "IN THE ULTIMATE CLASSIC OF SCIENCE," "THE PRINCIPIA ITSELF." "I'LL TELL YOU WHAT HE DID." "LISTEN CAREFULLY." "HE SAID, "SOUND TRAVELS 979 FEET EACH SECOND," ""NOT THROUGH THE AIR," "BUT THROUGH THE SPACE BETWEEN THE MOLECULES OF AIR."" "IT ACTUALLY GOES FURTHER IN EACH SECOND" "BECAUSE THE MOLECULES THEMSELVES TAKE UP SPACE." "HOW MUCH DO THEY TAKE UP?" "HE SAID, "WE KNOW THAT THE DENSITY OF AIR" "IS 470 TIMES LESS THAN THE DENSITY OF WATER."" "IF WE IMAGINE A VOLUME LIKE THIS CONTAINING AIR," "THAT AIR COULD BE CONDENSED INTO 1/470 OF THAT VOLUME." "THEN THE LINEAR DISTANCE IT TOOK UP" "WOULD BE 1/9 OF THE ORIGINAL LINEAR DISTANCE." "THE EXTRA DISTANCE THE SOUND TRAVELS IN 1 SECOND" "IS 979 DIVIDED BY 9, WHICH IS AN EXTRA 108." "IF HE ADDS THAT TO THIS, WE GET 1,088 FEET PER SECOND." "THAT'S CLOSER, BUT NOT GOOD ENOUGH FOR NEWTON." "HE SAYS, "WELL, AIR IS 10% WATER VAPOR."" "HE DOESN'T SAY HOW HE KNOWS THAT." "THE WATER DOESN'T PARTICIPATE IN THIS PROCESS." "HE DOESN'T SAY WHY." "WE SHOULD HAVE DIVIDED BY THE SQUARE ROOT" "OF 9/10 OF THE DENSITY OF AIR." "THE OTHER 1/10 IS WATER." "WE MUST ADD TO THIS 1,088 DIVIDED BY THE SQUARE ROOT OF 0.9." "THAT'S AN ADDITIONAL 5%, ABOUT 55 FEET." "IF HE ADDS 55 TO THIS, HE GETS 1,143 FEET PER SECOND," "COMPARED TO 1,142 FEET PER SECOND." "AND NOW, NEWTON WAS SATISFIED." "THAT'S HOW SIR ISAAC NEWTON MADE SCIENCE AND REASON" "TRIUMPH OVER MAGIC AND THE OCCULT." "I'LL SEE YOU NEXT TIME." "THEREALREASON FORTHEDISCREPANCY" "BETWEEN NEWTON'SCALCULATION" "ANDTHEMEASURED SPEEDOFSOUND" "ISTHATAIRISHEATED WHENIT'SCOMPRESSED" "CAUSINGITTO SPRINGBACK SLIGHTLYFASTER." "THISSUBTLEEFFECT WASN'TDISCOVERED" "UNTILA CENTURY AFTERNEWTON'SDEATH." "CAPTIONING PERFORMED BY THE NATIONAL CAPTIONING INSTITUTE, INC." 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