"Annenberg Media" "¶" "WHENA TORQUEACTS ONA SPINNINGOBJECT," "THE ANGULAR MOMENTUM CHANGES." "THERATEOF CHANGE OFANGULARMOMENTUM" "ISEQUALTO  THEAPPLIEDTORQUE." "UNDER A TORQUE'S INFLUENCE, A SPINNING OBJECT PRECESSES." "WE'VE NOW MASTERED" "THE THREE GREAT CONSERVATION LAWS OF MECHANICS." "IN A WORLD THAT SEEMS FULL OF CHANGE," "THOSE THREE THINGS ARE THE SAME NOW" "AS THEY'VE ALWAYS BEEN AND ALWAYS WILL BE FOREVER" "ENERGY, MOMENTUM, AND ANGULAR MOMENTUM." "THERE'S SOMETHING STRANGE ABOUT THOSE LAWS." "ISAAC NEWTON, WHO GAVE US ALL OF MECHANICS," "NEVER HIMSELF THOUGHT OF THE CONSERVATION LAWS." "THEY COME FROM HIS GREAT GIFT TO US," "F = ma." "BUT HE NEVER EXTRACTED THEM." "IT'S AS IF HE PURPOSELY LEFT SOMETHING" "FOR SOMEBODY ELSE TO DO." "THERE'S ANOTHER SMALL MYSTERY ABOUT NEWTON AND HIS LAWS." "HE BASED HIS MECHANICS ON THREE LAWS," "BUT WE ONLY SEEM TO USE ONE OF THEM." "EVERYTHING WE DO SEEMS TO COME FROM F = ma." "I SUSPECT THOSE TWO MYSTERIES ARE RELATED." "I THINK NEWTON HAD AN INKLING ABOUT CONSERVATION," "AND THAT'S WHAT HIS THIRD LAW IS ALL ABOUT." "TAKE THE CASE OF ENERGY." "ENERGY IS NEVER CREATED OR DESTROYED," "BUT IT CAN FLOW FROM ONE PLACE TO ANOTHER." "THAT'S CALLED WORK." "WORK IS A FORCE ACTING THROUGH A DISTANCE." "IF THERE'S FORCE ON ONE BODY," "THERE MUST BE THE REVERSE FORCE ON ANOTHER BODY." "THAT'S NEWTON'S THIRD LAW." "WHEN WORK GOES INTO ONE BODY, IT COMES OUT OF SOMETHING ELSE." "THAT'S HOW ENERGY IS CONSERVED." "OR MOMENTUM." "FORCE IS THE RATE OF CHANGE OF MOMENTUM." "IF A FORCE CAUSES ONE BODY'S MOMENTUM TO CHANGE," "THE REVERSE FORCE MUST BE ACTING ON ANOTHER BODY," "CAUSING ITS MOMENTUM TO CHANGE IN THE OPPOSITE DIRECTION." "THAT'S WHY MOMENTUM IS CONSERVED." "THE SAME IS TRUE OF ANGULAR MOMENTUM." "TORQUE IS EQUAL TO" "THE RATE OF CHANGE OF ANGULAR MOMENTUM." "A TORQUE ON ONE BODY IMPLIES A REVERSE TORQUE ON ANOTHER." "ANGULAR MOMENTUM FLOWS FROM ONE BODY TO ANOTHER," "AND ANGULAR MOMENTUM IS CONSERVED." "ALL THREE CONSERVATION LAWS CAN BE THOUGHT OF" "AS COMING OUT OF NEWTON'S THIRD LAW." "OUR SUBJECT FOR TODAY, ONCE AGAIN," "HAS TO DO WITH TORQUES AND ANGULAR MOMENTUM." "AS A MATTER OF FACT," "IT'S TIME WE HAD A LITTLE TORQUE." "[GROANS AND GIGGLES]" "HI, MISTER." "HI." "MY TIRE IS FLAT." "SURE IS." "CAN YOU FIX IT?" "SURE." "COME BACK IN 1/2 HOUR." "LONG BEFORE THERE WAS THE BICYCLE," "THERE WAS THE WHEEL ITSELF." "AND LONG BEFORE THAT, THERE WAS SIMPLY THE FOOT." "FEET TRANSPORT THEIR BEARER," "UNDER NORMAL CONDITIONS AND WITHOUT TOO HEAVY A LOAD," "ABOUT 5 KILOMETERS PER HOUR." "FEET OPERATE BY MAN, WOMAN, OR CHILD POWER." "THE ADVANCE OF CULTURE CAN BE TRACED ALONG THE PATH" "OF RAPIDLY IMPROVING TRANSPORTATION SYSTEMS." "BEFORE FINGERS DID THE WALKING," "HUMANS CALLED ON BEASTS OF BURDEN." "BEASTS AND BURDENS DIFFERED IN DIFFERENT CULTURES." "BUT FROM ANCIENT TIMES ONWARD," "WHILE THOSE WHO RODE MIGHT HAVE BEEN BEASTLY," "HUMANS HAD A WAY OF STEADILY ADVANCING CULTURE." "INCREASINGLY, THEY SAVED TIME IN THEIR ENDEAVORS" "AND WEAR AND TEAR ON THEIR FOOTGEAR." "BUT NO MATTER HOW, AND HOW FAR," "HUMAN DESTINY IS BOUND TO TRAVEL." "IT REALLY GOT ROLLING WITH THE WHEEL." "ABOUT 4000 B.C.," "THE SUMERIANS OF MESOPOTAMIA PROBABLY INVENTED THE WHEEL." "THEIRS MIGHT HAVE BEEN A TREE SLICE" "OR FLAT PIECES OF WOOD TIED IN A CIRCLE," "BUT ONE THING ABOUT WHEELS HASN'T CHANGED" "WHEELS ARE DESIGNED TO SPIN." "THERE'S NOTHING SPECIAL ABOUT A WHEEL THAT'S NOT SPINNING." "[TELEPHONE RINGS]" "FORGET TO HOLD IT UP, AND IT FALLS OVER." "THE FORCE OF GRAVITY" "TIPS THE WHEEL DOWN." "IN OTHER WORDS," "IF THE WHEEL DOESN'T SPIN," "IT HAS NO PLACE TO GO BUT DOWN." "A SPINNING WHEEL IS ANOTHER MATTER." "A SPINNING WHEEL HAS ANGULAR MOMENTUM," "AND THERE'S THAT STRANGE TWIST WHEN MOMENTUM IS ANGULAR." "IT'S NOT THE FORCE THAT CHANGES ANGULAR MOMENTUM." "IT'S THE TWIST." "IF r x F = 0," "THE ANGULAR MOMENTUM IS CONSERVED." "OBVIOUSLY, NOT ALL FORCES BEHAVE THAT WAY." "FOR EXAMPLE, TO OPEN VALVES OR TO GET WHEELS ROLLING," "TWIST IS JUST WHAT'S NEEDED." "TORQUE IS THE TWISTING FORCE THAT CAUSES ROTATION," "AND IT'S EQUAL TO r x F." "BUT A SPINNING WHEEL IS ALREADY ROTATING." "IT HAS ANGULAR MOMENTUM TO START WITH." "TORQUE CAN MAKE ANGULAR MOMENTUM CHANGE," "BUT IN A DIFFERENT WAY." "NOW GRAVITY CAN PLAY A STRANGE TRICK." "ITS FORCE IS DOWNWARD, BUT THE TORQUE IS SIDEWAYS." "ACCORDING TO THE EQUATION TAU = dL/dt," "THE ANGULAR MOMENTUM WILL ROTATE SIDEWAYS," "AND RATHER THAN FALL DOWN," "SO WILL THE WHEEL ITSELF." "SO IN A ROUNDABOUT WAY," "IT'S EASY TO ILLUSTRATE THE FACT" "THAT A SPINNING WHEEL DOESN'T FALL." "BUT BEYOND THIS EXAMPLE OF LIFE COPYING ANIMATION," "WHAT'S REALLY GOING ON HERE?" "WHAT KEEPS THE WHEEL FROM FALLING?" "WHENGRAVITYMAKES ANONSPINNINGWHEELFALL," "THESPOKESPUSH THE TOP OF THE WHEEL OUTWARD" "RATHERTHANDOWNWARD," "WHICHCREATES ACOMPONENTOF VELOCITY" "INTHEOUTWARDDIRECTION." "THESAMETHINGHAPPENS ATTHEBOTTOM," "BUTINWARDINSTEADOFOUTWARD." "THESAMETHINGHAPPENS" "WHENTHEWHEELSPINS." "NOW,HOWEVER," "WHENTHEOUTWARDVELOCITY BUILDSUP," "IT'SATTHESIDEOFTHEWHEEL," "OUTWARDONONESIDE" "ANDINWARDON THEOTHER." "EACH SPOKE ADDS ITS OWN PUSH" "ATTHETOP," "CAUSINGA JOGAT THESIDE." "SOTHENETRESULT" "ISN'TDOWNWARDMOTION." "IT'SSIDEWAYS." "ONCE THE WHEEL STARTS GOING AROUND THAT WAY," "IT'S CALLED PRECESSING." "A SPINNING BICYCLE WHEEL AND A SPINNING TOP" "HAVE MUCH IN COMMON." "A NONSPINNING TOP" "ISN'T INCLINED TO BALANCE ON ITS POINT." "ON THE OTHER HAND," "A SPINNING TOP DOESN'T TIP OVER." "INSTEAD, GRAVITY PRODUCES A DIFFERENT KIND OF MOTION" "PRECESSION." "WHETHER IT'S SPINNING OR NOT," "THE TOP ACTS AS IF ALL ITS MASS" "WERE CONCENTRATED AT ITS CENTER," "A POINT CALLED" "THE CENTER OF MASS." "IF THE TOP IS TILTED," "EVEN A LITTLE BIT," "THE RESULT IS A TORQUE." "WHEN THIS HAPPENS" "TO A SPINNING TOP," "THE TORQUE" "NUDGES THE ANGULAR MOMENTUM" "OF THE TOP" "AROUND IN A CIRCLE." "ROUND SHE GOES," "WITH A LITTLE FRICTION" "CAUSING HEAT AT THE TOP'S POINT." "WHENEVER HEAT IS PRODUCED," "A CERTAIN AMOUNT OF ENERGY IS LOST." "THAT'S BECAUSE HEAT," "WHICH IS THE RANDOM MOTION OF MOLECULES," "IS ANOTHER FORM OF ENERGY." "ABSOLUTELY EVERYTHING ON EARTH HAS A CERTAIN AMOUNT OF HEAT," "AND THEREFORE, A CERTAIN AMOUNT OF ENERGY." "AND NO MATTER WHERE THAT ENERGY RESIDES" "WITHIN A CRACKLING FIRE" "OR A CRACKLING FLOE OF ICE" "OR THE POTENTIAL ENERGY OF A GYROSCOPE" "THAT SEEMS TO RESIST GRAVITY" "ALL ENERGY, NO MATTER ITS FORM, IS ALWAYS CONSERVED." "THAT'S THE CONSERVATION OF ENERGY." "IT'S A PROFOUND LAW OF PHYSICS AND SO UNIVERSAL," "IT CAN BE SEEN IN THE PRECESSION OF A TOY." "HERE, TOO, HEAT'S BEING PRODUCED." "SOME ENERGY COMES FROM LOWERING THE CENTER OF MASS OF THE TOY," "WHICH SINKS LOWER" "AS THE OBJECT'S PRECESSION GETS LARGER." "BUT DESPITE THE LOSS OF ENERGY," "ROTATION CONTINUES WITH REMARKABLE STABILITY." "ROUND SHE GOES," "AND ROUND AND ROUND SHE'LL CONTINUE TO GO" "UNTIL SOMETHING INTERRUPTS THE PRECESSION." "OF COURSE, BEFORE SOMETHING INTERRUPTS THEIR PRECESSION," "TOPS AND TOYS CAN PRECESS" "IN THE MOST AMAZING AND AMUSING WAYS." "BUT A TOY GYROSCOPE," "PERHAPS LIKE THE CHILD WHO PLAYS WITH ONE," "CAN GROW UP" "TO BECOME A MATURE INSTRUMENT OF SCIENCE." "WHILE THIS GYROSCOPE MAY BE FUN TO WATCH," "IT'S NO TOY." "IT'S NOT DESIGNED TO PLAY GAMES." "IT'S DESIGNED NOT TO PRECESS." "IF A GYROSCOPE IS BALANCED AT ITS OWN CENTER OF MASS," "THE FORCE OF GRAVITY WON'T MAKE IT PRECESS." "EVEN IF ITS SUPPORTS SWIVEL IN ALL DIRECTIONS," "THE AXIS REMAINS STABLE" "AND KEEPS THE GYROSCOPE POINTED IN THE SAME FIXED DIRECTION." "THE IDEA HERE IS TO DESIGN A GYROSCOPE" "THAT HARDLY PRECESSES AT ALL." "AND EVEN IN A TOY STORE," "THE IDEA OF A SOPHISTICATED GYROSCOPE" "CAN HAVE SERIOUS IMPLICATIONS." "IN THE REAL WORLD, AIDED BY GYROSCOPES," "ANY DEVIATION FROM A PREDETERMINED HEADING" "IN AN AIRCRAFT OR SUBMARINE" "CAN BE DETECTED AND CORRECTED AUTOMATICALLY." "IN THE PAST, IF A PLANE RISKED A POLAR ROUTE," "IT HAD LITTLE CHANCE" "OF LANDING ON EVEN THE RIGHT CONTINENT." "CLOSE TO THE POLE," "A MAGNETIC COMPASS IS NO USE AT ALL." "THESE DAYS, SET STRAIGHT BY GYROSCOPES," "AIRLINES ROUTINELY FLY OVER THE POLES." "THE GYROSCOPE'S VALUE ISN'T LIMITED TO THE POLES," "NOR EVEN TO THE EARTH'S ATMOSPHERE." "IN OUTER SPACE," "WHERE PRECIOUS TIME AND ROCKET FUEL" "MUST BE USED WISELY," "GYROSCOPES ARE, MORE THAN EVER, VITAL ELEMENTS OF NAVIGATION." "WHETHER IN THE WATER OF THE EARTH..." "THE CLOUDS ABOVE IT..." "OR IN OUTER SPACE," "A GYROSCOPE'S VALUE DEPENDS ON ITS ABILITY TO SPIN" "IN A FIXED DIRECTION WITHOUT PRECESSING." "GYROSCOPE DESIGNERS REDUCE PRECESSION" "BY ELIMINATING TORQUES AND IMPROVING DESIGN." "WHENANOBJECTPRECESSES," "THETIPOF" "ITSANGULARMOMENTUMVECTOR" "MOVESIN" "UNIFORMCIRCULARMOTION" "WITH A CONSTANT ANGULAR SPEED" "CALLEDCAPITALOMEGA." "CAPITALOMEGA" "ISTHERATEOFPRECESSION." "THEEQUATIONSOF  UNIFORMCIRCULARMOTION" "SAYTHATv,  THERATEOF CHANGEOFr ," "ISOMEGATIMESr." "INTHESAMEWAY ,TAU ," "THERATEOF CHANGEOFL ," "ISCAPITALOMEGATIMESL." "SOOMEGAIS JUST TORQUEDIVIDEDBY L." "SINCE A GOOD GYROSCOPE HARDLY PRECESSES AT ALL," "THE BIKE WHEEL ISN'T GOOD FOR NAVIGATION." "IT PRECESSES TOO MUCH." "WHY?" "TORQUEISRx F." "SINCE THEY'RE PERPENDICULAR FORTHEBICYCLEWHEEL," "THE MAGNITUDE IS R TIMES F." "THEFORCE COMESFROMGRAVITY." "ANGULARMOMENTUM ISm TIMESrx v." "ALLTHEMASS ISATTHERIM ," "SOTHEMAGNITUDEOFL" "ISm TIMES THERADIUSOF THEWHEEL" "TIMESTHEVELOCITY OFTHERIM." "SINCEv ISOMEGAr," "THEPRECESSIONRATE" "IS THE DISTANCE TO THE PIVOT TIMESg" "DIVIDEDBY THEROTATIONRATEOFTHEWHEEL" "TIMES THE RADIUS OF THE WHEEL SQUARED." "THEGYROSCOPE WILLPRECESSLEAST" "IFIT'SSPINNINGFAST, IFTHEWHEELISLARGE," "ANDIFIT 'S CAREFULLYBALANCED." "IF ALL THOSE FACTORS ARE AT WORK," "A GYROSCOPE HOLDS ITS COURSE EXTREMELY WELL." "EXACTLY HOW WELL?" "THEY'RE NOT PERFECT, OF COURSE," "BECAUSE ANYTHING MADE BY HUMAN HANDS" "IS SUBJECT TO TINY IMBALANCES AND SLIGHT IMPERFECTION," "MECHANICAL OR OTHERWISE." "BUT THE BEST GYROSCOPIC GUIDANCE SYSTEMS" "COME PRETTY CLOSE TO PERFECTION." "IN FACT, THEY FEATURE GYROSCOPES" "THAT DRIFT AS LITTLE AS 100 SECONDS OF ARC PER DAY." "PRECISE AS THIS IS," "IT ISN'T THE BEST GYROSCOPE AROUND TODAY." "WHAT IS?" "WHAT IS THE BEST GYROSCOPE ON EARTH?" "ISAAC NEWTON HAD THE ANSWER." "IN FACT, HE WAS THE FIRST TO DISCOVER IT." "THE BEST GYROSCOPE ON EARTH IS THE EARTH ITSELF." "THE EARTH, AS NEWTON KNEW," "SPINS ON AN AXIS THAT'S TILTED AT 23 1/2 DEGREES," "WITH RESPECT TO THE PERPENDICULAR" "TO THE PLANE OF THE ECLIPTIC" "THE PLANE OF THE EARTH'S ORBIT AROUND THE SUN." "IN OTHER WORDS, AS SEEN FROM THE EARTH," "THE SUN SEEMS TO BE ORBITING IN A PLANE" "TILTED 23 1/2 DEGREES TO THE PLANE OF THE EQUATOR." "TWICE A YEAR, THE SUN PASSES DIRECTLY THROUGH" "THE PLANE OF THE EQUATOR." "THESE POINTS WHERE THE SUN INTERSECTS THE EQUATOR'S PLANE" "ARE CALLED THE EQUINOXES," "MEANING DAY AND NIGHT HAVE EQUAL LENGTH." "THESE POINTS HAVE LONG BEEN VITAL TO ASTRONOMERS." "FROM THE EARLIEST NIGHTS," "ASTRONOMERS HAVE OBSERVED THE PHENOMENON OF THE EQUINOXES." "THE CHINESE, THE GREEKS, THE BABYLONIANS, AND THE TURKS," "ACROSS TIME AND WITHIN THE GREATEST CIVILIZATIONS," "THEY SHARED A FASCINATION FOR THE EQUINOXES," "WHICH MARKED THE EXACT MOMENTS OF SEASONAL CHANGE." "THE EGYPTIANS, THE MAYANS, ALL THE ANCIENT WORLD" "HOWEVER DIFFERENT THEIR LANDS MIGHT HAVE BEEN," "THEY SHARED THE SAME SKY." "WHATEVER DIFFERENCES THEIR RELIGIONS HAD," "ANCIENT ASTRONOMERS LOOKED TOWARD THE HEAVENS" "WITH SOMETHING IN COMMON." "IN ONE WAY OR ANOTHER," "THEY CALCULATED THE PRECISE POSITION" "OF THE EQUINOXES." "BUT EVEN HEAVENLY LOOKS WERE DECEIVING." "THE EQUINOXES ARE NOT FIXED IN THE HEAVENS." "THEY DRIFT, A BIT EACH YEAR," "VERY SLOWLY TO THE WEST." "AND IN THE PRECISE PERPENDICULAR DIRECTION" "THOUGH THIS WENT UNNOTICED FOR THOUSANDS OF YEARS" "THE POLE STAR SEEMS TO DRIFT AS WELL." "NONETHELESS, ANCIENT ASTRONOMERS" "VIEWED THE POLE STAR DIFFERENTLY." "THEY SAW IT AS FIXED IN PLACE," "ABSOLUTELY AND ETERNALLY, LIKE A COSMIC MYTH." "IN CHINA, IT WAS RESPECTED AS A GODDESS," "WITH THE POWER TO PROLONG LIFE ITSELF." "ARABIC SCHOLARS VIEWED THE STAR AS EVIL." "THEY BELIEVED THE NORTH STAR" "HAD SLAIN THE GREAT SKY WARRIOR," "WHO FOREVER AFTER LAY IN A COSMIC COFFIN" "OUTLINED IN DETAIL BY THE BIG DIPPER." "BUT FOR ALL THE MYTHOLOGY SURROUNDING IT," "POLARIS HAS HAD PRACTICAL ASPECTS." "KNOWN AS THE LODESTAR, STEERING STAR, AND SHIP STAR," "IT HELPED SAILORS NAVIGATE THE SEAS." "THE EGYPTIANS SEEMED TO HAVE BUILT THE PYRAMID OF KHUFU" "IN LIGHT OF THE POLE STAR ITSELF," "WHICH WAS VISIBLE FROM THE BOTTOM" "OF ONE OF THE PYRAMID'S DEEP SHAFTS." "3,000 YEARS BEFORE CHRIST," "THE POLE STAR WASN'T THE POLARIS IT IS TODAY." "THE EGYPTIANS CALLED IT THU'BAN," "AND IT WAS A DIFFERENT STAR." "ACROSS TIME AND CHARTS OF ASTRONOMY," "POLARIS IS INCHING CLOSER TO THE POLE," "WHERE IT WILL COME CLOSEST IN THE 22nd CENTURY." "THE POLE STAR'S DRIFT" "IS RELATED TO THE PRECESSION OF THE VERNAL EQUINOX." "TONIGHT, THE VERNAL EQUINOX IS IN THE CONSTELLATION PISCES." "IT'S SLOWLY MOVING TOWARD THE CONSTELLATION OF AQUARIUS," "WHICH MEANS THAT CONTRARY TO CERTAIN REVOLUTIONARY NOTIONS" "OF THE 1960s," "THE AGE OF AQUARIUS WON'T COME FOR 400 YEARS." "400 YEARS AGO," "THE MOST REVOLUTIONARY MAN ON THE SCENE" "WAS NICOLAUS COPERNICUS." "IN 1543, DE REVOLUTIONIBUS PRESENTED AN EXPLANATION" "FOR THE PHENOMENON OF MIGRATION IN THE HEAVENS." ""THE PRECESSION OF THE EQUINOXES," HE WROTE," ""IS DUE TO THE AXIS OF THE EARTH" "SLOWLY TRACING OUT A CIRCLE."" "WHILE COPERNICUS UNDERSTOOD EQUINOX PRECESSION" "BETTER THAN ANYONE BEFORE HIM," "IT TOOK ISAAC NEWTON TO EXPLAIN IT FULLY." "HIS EXPLANATION FOR THE DRIFT OF THE EQUINOXES" "CAME FROM HIS DISCOVERY THAT THE EARTH IS A GYROSCOPE" "AND FROM HIS KNOWLEDGE" "THAT THE EARTH ISN'T PERFECTLY SPHERICAL." "IF IT WERE, THE SUN WOULD EXERT NO TORQUE ON IT." "LIKE ANY GYROSCOPE, THE EARTH PRECESSES." "ROTATING ABOUT ITS AXIS" "CAUSES THE EARTH TO BULGE SLIGHTLY AT THE EQUATOR." "THE SUN'S GRAVITY," "ACTING MOST STRONGLY ON THE NEAREST BULGE," "EXERTS A SMALL TORQUE ABOUT THE EARTH'S CENTER" "WHEN THE SUN IS ON ONE SIDE OF THE EARTH," "AND WHEN THE SUN IS ON THE OTHER SIDE," "A TORQUE IN THE SAME DIRECTION." "THE TORQUE IS TINY," "BUT IT'S ENOUGH TO MAKE THE EARTH'S AXIS OF ROTATION" "PRECESS VERY SLOWLY." "VERY SLOWLY, INDEED." "ONE COMPLETE LOOP TAKES ABOUT 26,000 YEARS." "COMPARE THAT TO THIS GYROSCOPE," "WHICH PRECESSES THROUGH A COMPLETE CYCLE" "EVERY FEW SECONDS." "COMPARED TO THE EARTH," "A BIKE IS NO MATCH AS A GYROSCOPE." "IT'S HARD TO IMAGINE" "A BETTER GYROSCOPE THAN THE EARTH," "AND HARDER STILL TO IMAGINE RIDING IT HOME FOR LUNCH." "THE GYROSCOPE IS A STRANGE AND BEGUILING INSTRUMENT." "BUT WHAT I ALWAYS FIND MOST AMAZING" "IS THAT FACT THAT NEWTON UNDERSTOOD IT" "AND WAS ABLE TO EXPLAIN THE PRECESSION OF THE EQUINOXES." "ANYONE ELSE WHO HAD DONE THAT AND ONLY THAT" "WOULD BE REMEMBERED TODAY." "BUT FOR NEWTON, IT'S LOST IN THE WELTER" "OF HIS ACCOMPLISHMENTS." "NEWTON HAD A YOUNGER FRIEND NAMED EDMUND HALLEY." "ONE DAY IN 1684, HE CASUALLY TOLD HALLEY HE HAD DISCOVERED" "THAT AN INVERSE R-SQUARED LAW OF GRAVITY" "WOULD GIVE ORBITS FOR THE PLANETS" "IN THE FORM OF CONIC SECTIONS." "IT'S HARD TO IMAGINE" "HALLEY'S REACTION TO THAT REVELATION." "BEING NEWTON'S FRIEND COULDN'T HAVE BEEN VERY RELAXING" "IN THE BEST OF CIRCUMSTANCES," "BUT NEWTON HAD TOLD HIM HE'D DISCOVERED" "THE KEY TO THE UNIVERSE." "HALLEY PREVAILED UPON NEWTON TO PUBLISH HIS DISCOVERY," "WHICH NEWTON ULTIMATELY DID." "IT TURNED OUT TO BE TRUE." "NEWTON HAD DISCOVERED THE KEY TO THE UNIVERSE." "WE'LL TURN THAT KEY NEXT TIME." "PRECESSIONISTHERESULT" "OFA TORQUEAPPLIED TOA SPINNINGOBJECT." "THERATEOF PRECESSION ISDETERMINED" "BYTHEANGULARMOMENTUM OFTHEOBJECT" "ANDTHETORQUE." "THEEARTHITSELF ISA GYROSCOPE," "PRECESSING UNDER THE TOR(jE APPLIEDBYTHESUN ." "CAPTIONING PERFORMED BY THE NATIONAL CAPTIONING INSTITUTE, INC." "CAPTIONS COPYRIGHT 1985 CALIFORNIA INSTITUTE OF TECHNOLOGY," "THE CORPORATION FOR COMMUNITY COLLEGE TELEVISION, AND THE ANNENBERG/CPB PROJECT" "PUBLIC PERFORMANCE OF CAPTIONS PROHIBITED WITHOUT PERMISSION OF NATIONAL CAPTIONING INSTITUTE" "Annenberg Media" "¶" "For information about this and other Annenberg Media programs call 1-800-LEARNER and visit us at"