It’s summer, and love is in the air…also, love-15, love-30, game, set, and match. Yes, it’s tennis time, and the air is filled with the distinctive “thwock” of balls hitting racquets and balls hitting courts, plus the occasionally equally distinctive sound made by a player who just missed an easy return.
Of course, being the studious science writer that I am, when I look at people playing tennis I don’t see an entertaining game of serving and volleying, but an entertaining interplay of a variety of scientific principles.
But first, a little historical background…
The word “tennis” comes from the Old French name for the game, “tenetz.” Late-13th-century Paris had a tennis-like game, played among the upper classes (the lower classes generally being too busy with little things like surviving to play games). The Italians and Greeks had a similar game at the same time. The French called their game “jeu de paume,” or “game of the palm,” because they used their hands to strike the ball. Racquets came along later. In the late 14th century the British aristocracy also started playing the game, which by this time was similar to badminton. It’s still played today: in the U.S. they call it “court tennis,” while in England it’s called “real tennis.”
In 1873 a British army officer, Major Walter Clopton Wingfield, drew on his knowledge of “real tennis” and invented a brand-new game: “lawn tennis,” which he patented. (Well, actually, he called it “sphairistik‚,” a Greek term meaning “playing at ball,” because he liked to claim he’d modelled it on an ancient Greek game–but nobody believed him and his name for the sport, fortunately, never caught on.) The game found its way to Bermuda that same year and from Bermuda was brought to the U.S. by a vacationing woman from Staten Island, New York, Mary Ewing Outerbridge.) It didn’t take long for tennis to spread to Canada, too.
Rules and standards varied widely for the first few years; in the U.S., the United States Lawn Tennis Association was formed in 1881 to standardize rules and equipment. Internationally, tennis is governed by the International Lawn Tennis Federation in London, founded in 1912.
Basic tennis equipment includes the ball, made of hollow rubber covered with a wool composition, between six and seven centimetres in diameter and weighing between 57 and 58 grams, and the racquet, which can vary widely in shape and size (more on that later). The court can be made of grass, clay, concrete, wood composition matter, or any other hard, even substance.
To start a game, a player tosses the ball in the air and hits it over the net–and immediately, science comes into play.
The goal of the serve is to impart as much energy as possible to the ball, which has to be accelerated from an essentially stationery position to a speed (in the case of the world’s top male players) of 200 kilometres an hour or more in an instant. That energy comes from the body of the player. One tennis pro compared it to a linear accelerator, which accelerates sub-atomic particles by moving them down a long tube, adding a little bit of energy every time the particle passes another set of magnets. In the case of the player, a little bit of power is added from each of various motions: bending knees, throwing the racquet head up over the shoulder, twisting the torso, snapping the wrist…all of these movements contribute to moving the racquet head through the air as fast as possible. The faster the racquet head is moving when it hits the ball, the faster the ball will be accelerated. Gravity helps: in a sense the player is throwing the weight of his body against the ball.
When the racquet hits the ball, two things happen. Racquets are made out of various materials, and strung with either gut (made from the intestines of sheep and goats) or nylon. These flexible materials bend with the impact of the ball, but then snap out again, imparting a little extra speed. So flexible strings are good. You might think a flexible racquet, one that would bend and snap forward just like the strings, would also be good, but it’s actually bad: the reason is that the racquet takes a much longer time to snap back into shape. By the time it does, the ball is already gone. Instead of imparting energy to the ball, a flexible racquet actually drains some energy out of the swing.
This has been one of the driving forces behind recent developments in tennis racquets. The “wide-body” racquets of today are designed to maximize stiffness. At the same time, new materials like graphite and graphite composites have allowed manufacturers to combine stiffness with lower weights (a top-of-the-line graphite racquet can weigh anywhere from two to four ounces less than the old wood frames that were the standard for decades). Lower weight allows the player to swing the racquet faster, and therefore impart more energy to the ball.
Another big change in racquets occurred in 1976 when a new aluminum racquet called the Prince appeared. It had a hitting area of 130 square inches–almost twice that of ordinary wooden racquets. Tennis sanctioning bodies had set no rules governing the size of tennis racquet heads, probably because they couldn’t imagine any materials strong enough to bear the much greater stresses a large head would be under. (After giant racquets started to appear, however, the International Tennis Federation limited the hitting area to 178 square inches.)
Today, racquets come in a variety of sizes, from midsize to oversize plus. Large heads also increase ball speed because the longer spans of strings flex more.
Racquet manufacturers also continue to work on the “sweet spot” of their racquets, trying to move it higher and higher, because the highest part of the racquet head moves faster than the lower part during a swing. The “sweet spot” is that point which yields the most power and stability with the least shock and vibration.
Okay, so the ball has been hit. What happens next?
Probably, the ball has had some “English” put on it: that is, it’s spinning. There’s higher air resistance on the side of the ball that’s spinning into the airflow than there is on the other side; the ball gets pushed in the direction of the lower resistance. So a backspinning ball will tend to rise, a forward spinning ball to sink, a ball spinning clockwise will go right, and a ball spinning counterclockwise will go left. This spin is imparted by the strings of the racquet (and, of course, the way the player swings the racquet). Although most tennis racquet strings are smooth, some nylon strings are specially shaped to increase their “bite” into the ball, making it easier to apply English.
Once the ball gets across the net, it bounces: it deforms as it hits the court, then it springs back into shape. In more scientific terms, its kinetic energy is momentarily transformed into potential energy, stored in its deformed rubber shell; when the rubber snaps back into its preferred shape, that energy is turned back into kinetic energy, and the ball leaps up into the air again. The angle at which it bounces is also affected by the way in which its spinning, since that gives it a slight impetus to go one way or another. The court substance will also effect the way the ball bounces; a springier substance, such as turf, absorbs more of the ball’s energy than a hard surface like concrete. As well, no matter how well groomed, has many more surface irregularities that can slightly alter the direction of the ball’s bounce.
Now its up to the receiving player to return the ball. Everything we’ve mentioned about the racquet and ball still holds true, but the receiving player has another challenge: he has to hit a moving ball instead of a stationary ball. This requires him to launch himself across the court to intercept it. If he misjudges, he’ll miss the ball. Even if he hits it, he may find himself out of position to return it on its next trip across the net. The reason? Inertia. A body in motion tends to remain in motion. If a player is running full tilt across the court, he has to expend a great deal of energy to stop his forward motion and reverse direction. If his opponent is able to place the ball well behind him, he may not have time to make that change.
Friction is also an important part of tennis: it’s what keeps the racquet from slipping out of the players hand and the player from falling down every time he has to move. Shoes with “good grip” are those that maximize friction between the player and the court.
No discussion of the science of tennis would be complete without its best known medical syndrome: “tennis elbow,” known to doctors as “lateral epicondylitis.” It’s an inflammation caused by microscopic tears in the tendons of the elbow. The name is a bit of a misnomer: only five percent of cases are caused by playing tennis. Most are found among workers who have to make a gripping motion repeatedly: carpenters, violinists, jackhammer operators. However, tennis elbow was first identified in 1882 and got its name because, at the time, it was easy to see, at a garden party, who the tennis players were: they winced every time they had to raise a teacup.
Of course, the best way for a tennis player to deal with tennis elbow would be to quit playing tennis for a while, but that, for dedicated tennis players, is clearly unthinkable, and so they wear ice packs and take anti-inflammatory drugs and put on forearm braces and try to change their strokes or maybe their racquets.
For the true tennis fanatic, a little thing like “lateral epicondylitis” isn’t enough to keep them the game they “love.”
