The Rocket Science Of Tennis And Its — страница 2

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opponent can do to guide it or change its path. There are three forces acting on the ball during its flight; gravity, air resistance, and the Magnus force which causes the ball to curve. The force due to gravity (mg) is always pointed straight down toward the Earth. Air resistance slows the ball, and in the range of speeds encountered in tennis, the force it causes is proportional to the square of the ball?s speed. For example, a ball moving at 50 m.p.h. will encounter four times as much air resistance force than that of a ball moving at 20 m.p.h. Wind also creates an air resistance force, which can be analyzed in a similar manner. Because air resistance force is proportional to the square of the speed, a crosswind of 20 m.p.h. will exert four times as much force on the ball as a

10 m.p.h. crosswind, and a 30 m.p.h. crosswind provides a force nine times as strong as the 10 m.p.h. wind. This is obvious when a tennis player tosses the ball up for a serve if there is a brisk breeze. The Magnus force is at right angles to the direction that the ball is moving and is proportional to how fast the ball is spinning. It is also proportional to the square of the ball?s speed. Because of these factors, it is very important for tennis players to be able to observe these certain characteristics. They must be able to think critically to place the shot in the correct side of the opponent?s court. There are many ways in which a player may hit the tennis ball. Choosing a good strategy and position, hitting high-percentage shots, and using the proper equipment may help the

player win more points. The angle of the racket face and the direction of the racket velocity at the instant of contact between the ball and the racket determine where exactly the ball will go. When a player stands at the forehand corner of the court and attempts to return a shot to the center of the challenger?s court with a forehand drive, the shot will go crosscourt if the player swings a little early. If he or she swings a little late, the shot will go down the line (Cantin 6). The swing of a tennis racket can be described as the arc of a circle. At the second that the player hits the ball, the racket is in a certain position in the arc. Thus, the face of the racket is pointing in a certain direction, and at that moment the racket is moving tangent to the arc. The angular

error of the racket is given by the formula 57 x timing error x (ball speed + racket speed)/ swing radius. This means that the worse the timing error, the larger the angular error. This error decreases as the swing radius increases, but it increases as the racket speed and the speed of the approaching ball increase. This attributes to the knots in a tennis player?s stomach as the opponent puts increased pressure on them. Increasing the radius of swing however, will improve the player?s accuracy and control. If the player keeps a firm wrist and uses his or her shoulders as the pivot point for his or her shots, he or she will double the radius of his or her swing and will reduce by half the horizontal angular error caused by the timing error associated with that shot (Brody 119).

The three most popular techniques in the sport of tennis include topspin, backspin, and sidespin. Topspin is, by far, the most challenging and requires a greater appreciation of physics. Topspin on a tennis ball is usually called the powerspin. The difference between a shot with topspin and a shot without topspin is rotational motion on the shot with topspin as well as translational motion. If the face of the racket is oriented so that it is perpendicular to the direction of the racket?s motion, the resulting shot will have little or no spin. So how do you generate a lift and spin on the tennis ball? Lift is generated by creating a pressure difference and deflecting the flow. To create a pressure difference on the ball, it needs to move more fluid around one side than the other.

Spinning the ball will set up the imbalance, thus making the pressure difference. When the tennis ball rotates, the fluid that is in contact with the ball?s surface tends to rotate with the ball. The air next to the air on the surface tends to do the same thing. Far from the ball, this rotation does not affect the surrounding air. Very close to the ball, however, these fluid layers make up what is called a boundary layer. Consider the topspin stroke; if the ball doesn?t rotate as it flies through the air, then both the top and bottom sides of the ball meet the air rushing over it at the same speed. Relative to the ball, the top of the ball in topspin spins forward into the oncoming air. There is more movement of air towards the bottom surface. Now, more fluid needs to pass