SI Vault
Coles Phinizy
December 23, 1968
Bob Beamon knew that his jump was superb, probably a new record. But 29 feet? He fell to his knees. Here is an anatomy of that famous leap
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December 23, 1968

The Unbelievable Moment

Bob Beamon knew that his jump was superb, probably a new record. But 29 feet? He fell to his knees. Here is an anatomy of that famous leap

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Although part of the stadium crowd never saw the jump, by midnight around 40 million Americans back home had seen it, at normal speed and in slow motion, on ABC television. Track and field devotees—the statistical buffs in particular—are still savoring the moment, ruminating on it. It is without a doubt the tastiest single morsel of trackery that ever came their way—a tidbit so rich that it is difficult to digest. In this day, when a fractional improvement in any event is hard to come by, Beamon had pushed the long-jump record out from 27'4�" to 29'2�"—nearly two feet. In the past 50 years the world's best jumpers collectively had not advanced the mark much farther than Beamon did with one long jump. Beamon, in effect, had taken off into thin air in the year 1968 and landed somewhere in the next century.

Although it is no solace to other jumpers now faced with the futility of trying to overtake him, Bob Beamon admits that when he "put it all together," he did so at just the right time and under ideal conditions.

Track coaches are hereby warned not to let their jumping prot�g�s read farther into this article. At this point we are going to try to tarnish Beamon's shining moment by explaining some of it away in terms of drag, frontal area, terrestrial variations and acceleration curves. Any youngster who takes off down a runway with a head full of such junk probably will never make it past 21 feet.

Before the 1968 Games many experts—athletes, coaches and allied noodlers—were aware that while endurance men would suffer at the 7,349-foot altitude of Mexico City, the men of explosive effort—the sprinters, weight throwers and jumpers—would likely profit on two counts. For one thing, because the earth is an asymmetrical mass with an irregular surface, the gravitational pull exerted on any object, be it a man or the weight he throws, varies from place to place. Mexico City is, so to speak, a light area, giving the athlete an advantage of about one-tenth of 1% over what he might expect, say, in Los Angeles. Such a gravitational advantage is only of feathery significance in a 29-foot jump.

For certain, the thin air of Mexico City did help long jumpers and triple jumpers and all sprinters except sprint swimmers. (In Mexico the sprint swimmers competed in fresh water as dense as it is anywhere, and luckily so. If the water, like the air, had been thinner in Mexico City, all the swimmers would have sunk.) How much advantage did the land sprinters and jumpers enjoy in Mexico City? There's the knotty problem. In this screaming age of technology, a good deal is known about the resistance that fluid mediums of various densities offer to nose cones, foils, hulls and other shapes traveling through them. Although there has never been much need for knowing the effect of air density on a runner flailing his arms and legs while poking along about 25 mph, here and there some work has been done. From these meager pickings and an inference or two derived from the performance of other competitors at Mexico City, it is possible to get a rough idea of how much benefit Beamon gained from the thin air. (The author of this piece recognizes that, despite the valuable outside help he has received, the proposition remains a tacky one, open to assault from all sides. The author promises that any nitpicker who writes in finding fault either with the suppositions used or conclusions reached will receive, in return, a box of dead spiders.)

Just before Beamon jumped, a weather station in the Olympic Stadium recorded a temperature of 23.5� C, a humidity of 42% and a barometric pressure of 577.8 mm. From this data the density of the air can be calculated to be about 24% less than on a typical track and field day at sea level. Since the gravity factor of the area is known and Beamon's weight at the time is known (160 pounds), and since the approximate frontal area of a Beamon-sized human is known (8 square feet), and since the drag coefficient of a moving man is known (about 1.0), a physicist can reasonably approximate what effect the thinner air had on Beamon's performance while he was in flight. Presuming his trajectory and horizontal speed at takeoff both to be identical to what he would ordinarily achieve at sea level, Dr. Peter Wegener, professor of applied science at Yale, grossly figures that the effect of lower air density while Beamon was in flight could account for five or 10 cm. of his total jump—or about three inches, to take the mean figure.

Logically, the distance any jumper can travel through the air depends very much on the speed he has attained when he takes off the board. Before a physicist could even roughly calculate the speed advantage Beamon might have had at the board in Mexico City, he would need some data that is not available, notably a fairly accurate idea of Beamon's rate of acceleration on the runway. There has been an acceleration study made of sprinters, but since a jumper does not bolt right out of blocks like a sprinter, the acceleration curve is undoubtedly different—and probably differs considerably from one jumper to another. It is known that world-class jumpers do not reach—indeed, cannot reach—maximum speed in a normal approach of 130 to 140 feet, such as Beamon uses. By running farther a jumper can reach a peak speed, but then, on reaching the board, he must suddenly change the action of his legs to get lift, and since there is internal drag in the tendon and muscle of every man—but, oh Lord, let's not get into that. Let us just say that over the years jumpers have gotten their best distance when they hit the board traveling about 95% of maximum. Since Beamon is capable of 9.5 seconds for 100 yards, when he hits the board at sea level he is going about 24 mph, and with the same effort in Mexico City's thin air he is going, at most, 1% faster.

Where, other than right out of a hat, does this theoretical increase of 1% come from? It is based on what other athletes did at Mexico City. In the long jump there were three other athletes in Beamon's class—Boston, Ter-Ovanesyan and Davies—but their performances prove almost nothing one way or the other. As if Beamon's first spectacular jump was not enough of a dampener for his three important rivals, before any of them took a jump the heavens opened and the rains came. Competing on a rainless day, five men bettered the world triple-jump record at Mexico City. The thin air for certain helped the triple jumpers, but the record they pursued was relatively easier to knock over. In off years not that many competitors exert pressure on the triple-jump mark, which makes it susceptible in times of intense competition like the Olympics. Although world dash records are rarely broken in Olympic Games, at Mexico City the winners of the 400-meter hurdles, the 400-meter dash and the 200-meter dash all ran faster than any man has run at sea level. Taking the winning times in all individual dashes and relays into consideration, and giving no credit for improvement either to the performers themselves or to the track, a 1% increase in speed, at the very most, can be attributed to the thinner air. Assuming all other factors equal, Dr. Wegener concludes that a 1% increase in speed could account at most for 20 cm. of Beamon's distance—about 7 7/8 inches. Thus, even beyond all the benefits gained from the location, Beamon still somehow hung it out there a good foot past the old mark.

The most satisfactory explanation of Beamon's astonishing long jump lies in an analysis of the event itself. Compared to other track and field events, the long jump is an anomaly. Veterans such as Ralph Boston concede that, in terms of technique and training effort, it is the simplest of the common events popular since the turn of this century. Since natural ability counts for a lot and technique for relatively less, there has always been an abundance of long jumpers but, curiously, a dearth of outstanding ones.

The event seems to defy progress. There has been less record-breaking in the long jump than in any other common event, and such improvements as have been made have come erratically. In 1901 an Irishman named Peter O'Connor jumped 24'11�", and although he advanced the record by only four inches, his mark lasted for 20 years until an American, Edwin Gourdin, jumped three and a quarter inches farther. For the next 14 years the record inched forward, until on a glorious, record-smashing day in 1935 Jesse Owens jumped 26'8�". Although Owens had pushed the record out only six inches, it was enough to last for 25 years.

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