•More SpeedFor an enhanced

Interactive NASCARgraphic, visIt

Ume.com

3 THE SPLITTER Thesmall shelf alongthe nose of the carcan be pushedfOlWard to Increasedownforce bydirecting more aironto the front end

Retracted splitter,less downforce

3 DOWNFORCEMoving air pushes all

. around the car. The air pushingdown creates additional grip.Faster air means more downforce

2 FRICTIONThe tires grip the track-'a result of the car's weightpushing down. Without It, thecar would skid

The rlght-slde tiresbear more weightduring turns, so theyget Inflated more

Lower pressureIncreases thetire's -footprlnt~­

Its grip on the track

2.THETIRES Each IsInflated differently.Most teams usenitrogen to avoidpressure changescaused whenwater moleculesInside a tire heatup during a race

More air strikes the wing,Increasing rear-end stability

~Olteellono1forees

1CENTRIPETAL FORCEThe -center-seeklng- forcepulling Inward to make thecar turn fights the car'sInertia, which wants the carto go straight. this createsthe feeling that the driver Isbeing pushed outward

Air flows smoothly over thewing, with less drag on the car

In previous years, NASCARteams built different carsfor different tracks. TodayNASCAR has one vehiclestyle for all tracks, but thatcar can be customized insmall yet critical ways to suitvarious racecourses and adriver's feel for the car'sperformance. Even minutechanges can mean thousandthsof a second-and the differencebetween winning and losing

••• and threeadjustmentscounter them

1THEWINGThe rear wing canbe adjusted up to16- from horizontal.Because each track Isdifferent, crews try tofind the perfect mix ofstability and drag foreach race

GRAPHIC BYLON TWEETEN

A car moving at 180 m.p.h. In a straightline will keep moving 180 m.p.h. In astraight line. That's the law of Inertia..But a NASCAR race is.a long series ofleft turns, and that's where the race iswon or lost. In a turn, drivers must'counter the car's inertia or they'll gostraight Into the wall. A successfulhigh-speed turn Is a delicatebalance of three powerful forcesacting all at once andconstantly changing. Toomuch or too little of anyforce could lead to.dlsaster

Three forces areat play in a turn •••

From Tile I'IoJlJICJ ~/NA.SCItR. by Di~ndr~ Lulie·rrlctky. Pubilihedwit h pelm Inion ofl)ullon, ~ member or Pcnculn Group (USA) Inc.Olooabyl)llndr~t...IUe·relecky

THE MORNING I DROVE THE

,. track at the Texas MotorSpeedway was a dreary Fri­day in February. Headingwest on Texas Highway I14,you get the feeling that you.aren't going anywhere. The

speedway-known to NASCAR fans simplyas TMS-dwarfs the surrounding town,but you don't see it until you reach thetop of a hill, and then there it is. TMS isa I.s·mile track that holds 200,000 specta·tors. Today I'd be one of the few who get toexperience things from the driver's side.

r would be driving today at up toISO m.p.h., which means that in I sec., I'dtravel almost three-quarters of a footballfield. I am a NASCAR fan and professor ofphysics at the University ofTexas at Dallas,so I grasp that in my brain. But that's notthe same as having a gut-level feel for it.

I arrived at the track and, after don­ning a fire suit and helmet, faced my firstchallenge: getting into the CaI. Stand·ing on the driver's side facing fprward,I swung my right leg into the window,got my other leg in and contorted into theseat. I'm Sft. 6 and very flexible. ThIn-timeDaytona 500 winner 6-ft.-S Michael Wal­trip either is a very limber guy or has ahigh tolerance for pain.

I felt abitclaustrophobic in thecar,moreso after an employee slipped the steering'wheel onto the column.The seat,whichen­veloped me, was low in the car. The b~ggestmodification to the car I'd be driving wasthe addition of a second seat, which todaywas occupied by my instructor, Paul.

Driving a stock car is nothing likedriving a street car really fast. The firstpart ofNewton's law ofinertia says a bodyat rest tends to remain at rest unless some­thing makes it move. The tires m9ve the

BY OIANORA LESLIE-PELECKY

ThePhysics ofNASCARA new book expiainswhy Sir Isaac Newtonwill always be thechampion of any track

40 TIME March 3, 2008 41

High speed, hard science For a while, Kyle Busch set, the pace in his No. 18 carat this month'~50th running ofthe Daytona S0D. In the end, though, Buschfin~shed fourth to winnerRytm Newman

chassis, the chassis moves the seat, andthe seat moves the driver. The second partofNewton's law dictates that a car movingat ISO m.p.h. keeps moving at ISO m.p.h.in the same directIon unless somethingcauses it to change its speed or direction.When you brake, your body keeps mov­ing forward until the seat belts exert aforce that stops you.

Just as you feel pushedbackwardwhenyou accelerate and forward' when youbrake, when you turn, you feel pushedtoward the outside of the circle. This isoften described as centrifugal force, butthere isn't ,really a force pushing yououtward. There is, however, an inward­pointing force called "centripetal" (or"center-seeking"). Centripetal force is thereason cars turn; the force you think youfeel pushing your body outward is actu­ally your body trying to obey Newton ~ndgo straight.

Whenyou accelerate,youfeel a"g"iorce.The g stands for gravity, which is mislead'ing because it's really a measure of accel­eration in any direction. A dropped objectaccelerates by 32 ft. per sec. (22 m.p.h.)every second, the standard measure of I G.Going from a to 70 in 5 sec., you experi­ence acceleration of 0.6 G. If you weigh160 lbs., that means you feel a force of96 additionallbs.-or 0.6 of body weight.A space-shuttle liftoff creates an accelera­tion of 3 Gs, which feeis like three peopleyour weight sitting on top ofyou. Duringa race, aNASCAR carcanacceleratefromoto200 m.p.h. in 12 sec., which is almost o.S G:

- Another force is exerted by air. Peoplesay Dale Earnhardt Sr. could "see" the airbecause he was s,o good at using aerody­namic's, but most of us don',t have thatability. Awind tunnel helps. The fans in atunnel produce a flow that acts like sheetsofair on top ofeach other. Pressure gaugesmeasure how hard the air hits the car. Thecar: itselfsits on a scale sensitive enough todetect the change in weight when a half­dollar is placed on the bumper.

A car's weight doesn't actually changewhen air moves over it; instead some ofthat air pushes down. The faster you go,the more downforce you get. Althoughmost of the air travels over the car, somegets beneath it. If the force of the air flow­ing underneath IS greater than the force ofthe air flowing above, you get lift, which isnot what you want. One of the reasons theback end of a stock car is higher than thefront is to help air escape.

Grip on the track is maintained by theflat area on each tire where it touches theground, called the "contact patch." Thecontact patch for a tire on my pickup truckis about 4 in. longby 7in. wide, or 28 sq. in.The contact patch for a Goodyear racing

, TIME March 3, 2008

, tire is,roughly 36 sq. in., which is ab~utthesize of a man's size-iI shoe. A typical tirepressure for a consumer vehicle is 301bs.per sq. in. (psi). On NASCAR cars, a tire maybe inflated to only 10 psi. But pressuresdon't stay low very long., When the air in a tire heats up-whichit does quickly as the tire rotates on thetrack-the molecules move faster, exert­ing more force. On passenger cars, tirepressure may change I psi for every roOFtemperature change. Your tires reachabout 160°F on the expressway, but thetires of a race car can reach 300°F. After along run, pressures in left-side wheels canincrease ro psi, and right side 20 psi.

None of this was on my mind when Itook my turn at TMS. We trundled downpit road, andwhenPaulmotioned, Ipressedthe clutch, shiftedinto third, then releasedthe clutch andstepped on the gas. Actually,Istepped on the gas andbralcebecause theyare so close together. Paul and I shouted,

Driving a stock car isnothing like driving astreet car really fast.I asked howfast wewent, figuring we hit120 m.p.h. In fact, weWeregoing 148 to 150

"Whoa!" I recovered, shifted cleanly intofourth ;md moved onto the track.

A NASCAR engine is optimized forspeed, so when you're puttering along atroo m.p.h., it chugs uncomfortably. Thesolution is to go faster. Paul gave me thethumbs-up, letting me increase my speed.As we completed laps, I started to appre­ciate what spotters mean when they telldrivers, "Get back in your rhythm." Therepetition of slow-constant-fast sequencearoun.d the corners is comforting. I learnedto brace myselfagainst the seat as we werethrown to the right around corriers.

As I passed the start-finish line on whatI thought was a particularly good lap (Paulhad given me a level-offhand signal on thebackstretch), I realIzed that the flagmanhad waved the white flag, signaling thatthis was the last lap. I had been warned toresist the urge to think, "This is the lastlap-nowIneedtogo reallyfast," butbeforeI finished that thought, the checkered flagwas waving andwe coasted into the pit.

It didn't matter that the cars don't havespeedometers, because I didn't take myeyes off the track once. I asked Paul howfast we went, figuring we hit 120 m.p.h. Infact; when he gave me the level-off sign,we were going 148 to ISO m.p.h. When Iclimbed out of the car, I realized my legswere wobbly and my heart was racing.As i exited TMS later in my own car and·headed back down Highway II4, I count­ed no fewer than five cars pulled over bythe police. I made a mental note to watchthe speedometer. ~ •

43