Question: To impart a spin on the ball which is parallel to its trajectory, how must the racket be swung?
About the article "Table tennis", section "Corkspin".

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This type of spin is almost exclusively employed in service, but it is also used from time to time in the lob at the professional level.
Unlike any of the aforementioned techniques, corkspin (sometimes referred to as "drill-spin") features a unique situation in which the axis of spin is more or less parallel to the trajectory of the ball.
This means that the Magnus effect will have little to no effect on the trajectory of a cork-spun ball.
Upon bouncing, the ball will dart right or left, depending on the direction of the spin, making it very difficult to return.
Although in theory this type of spin produces the most obnoxious effects, it is not as strategically practical as sidespin or backspin in terms of the limitations that it imposes upon the opponent during their return.
Aside from the initial direction change when bouncing, provided that it does not exceed the reach of the opponent, a cork-spun ball is easily countered with topspin "or" backspin.
Similar to a backspin stroke, the corkspin stroke has a lower maximum velocity, simply due to the contact angle of the racket when producing the stroke.
To impart a spin on the ball which is parallel to its trajectory, the racket must be swung more or less perpendicular to the trajectory of the ball.
This greatly limits the amount of forward momentum that can be transferred to the ball by the racket.
Corkspin is almost always mixed with another variety of spin, as it is less effective and harder to produce on its own.
Players are equipped with a laminated wooden racket covered with rubber on one or two sides depending on the grip of the player.
The official ITTF term is "racket", though "bat" is common in Britain, and "paddle" in the U.S.
The wooden portion of the racket, often referred to as the "blade", commonly features anywhere between one and seven plies of wood, though cork, glass fiber, carbon fiber, aluminum fiber, and Kevlar are sometimes used.
According to the ITTF regulations, at least 85% of the blade by thickness shall be of natural wood.
Common wood types include balsa, limba, and cypress or "hinoki," which is popular in Japan.
The average size of the blade is about 6.5 inches (16.5 cm) long and 6 inches (15 cm) wide.
Although the official restrictions only focus on the flatness and rigidness of the blade itself, these dimensions are optimal for most play styles.
Table tennis regulations allow different surfaces on each side of the racket.
Various types of surfaces provide various levels of spin or speed, and in some cases they nullify spin.
For example, a player may have a rubber that provides much spin on one side of his racket, and one that provides no spin on the other.
By flipping the racket in play, different types of returns are possible.
To help a player distinguish between the rubber used by his opposing player, international rules specify that one side must be red while the other side must be black.
The player has the right to inspect his opponent's racket before a match to see the type of rubber used and what color it is.
Despite high speed play and rapid exchanges, a player can see clearly what side of the racket was used to hit the ball.
Current rules state that, unless damaged in play, the racket cannot be exchanged for another racket at any time during a match. 
The Magnus effect explains commonly observed deviations from the typical trajectories or paths of spinning balls in sport, notably association football (soccer), table tennis, tennis, volleyball, golf, baseball, cricket and in paintball marker balls.
The curved path of a golf ball known as "slice" or "hook" is due largely to the ball's spinning motion (about its vertical axis) and the Magnus effect, causing a horizontal force that moves the ball from a straight-line in its trajectory.
Back-spin (upper surface rotating backwards from the direction of movement) on a golf ball causes a vertical force that counteracts the force of gravity slightly, and enables the ball to remain airborne a little longer than it would were the ball not spinning: this allows the ball to travel farther than a non-spinning (about its horizontal axis) ball.
In table tennis, the Magnus effect is easily observed, because of the small mass and low density of the ball.
An experienced player can place a wide variety of spins on the ball.
Table tennis rackets usually have a surface made of rubber to give the racket maximum grip on the ball, to impart a spin.
The Magnus effect is not responsible for the movement of the cricket ball seen in swing bowling, although it does contribute to the motion known as "drift" in spin bowling.
In airsoft, a system known as Hop-Up is used to create a backspin on a fired BB, which will greatly increase its range, using the Magnus effect in a similar manner as in golf.
In paintball, Tippmann's Flatline Barrel System also takes advantage of the Magnus effect by imparting a backspin on the paintballs, which increases their effective range by counteracting gravity.
In baseball, pitchers often impart different spins on the ball, causing it to curve in the desired direction due to the Magnus effect.
The PITCHf/x system measures the change in trajectory caused by Magnus in all pitches thrown in Major League Baseball.
The match ball for the 2010 FIFA World Cup has been criticised for the different Magnus effect from previous match balls.
The current ball is described as having less Magnus effect and as a result flies farther but with less controllable swerve. 
Spin bowlers or "spinners" impart rotation to the ball to get a batsman out.
The spin on the ball makes its movement hard to predict, particularly when it bounces, hence spin bowlers try to deceive batsmen into making a mistake.
Speed is not crucial in spin bowling, and spinners tend to bowl in the slow-medium to medium-slow range, around 45-55 mph.
There are two broad categories of spin bowling: wrist spin and finger spin. 
This type of spin is predominantly employed during service, wherein the contact angle of the racket can be more easily varied.
Unlike the two aforementioned techniques, sidespin causes the ball to spin on an axis which is vertical, rather than horizontal.
The axis of rotation is still roughly perpendicular, to the trajectory of the ball.
In this circumstance, the Magnus effect will still dictate the curvature of the ball to some degree.
Another difference is that unlike backspin and topspin, sidespin will have relatively very little effect on the bounce of the ball, much in the same way that a spinning top would not travel left or right if its axis of rotation were exactly vertical.
This makes sidespin a useful weapon in service, because it is less easily recognized when bouncing, and the ball "loses" less spin on the bounce.
Sidespin can also be employed in offensive rally strokes, often from a greater distance, as an adjunct to topspin or backspin.
This stroke is sometimes referred to as a "hook".
The hook can even be used in some extreme cases to circumvent the net when away from the table.