question: How do pool tables know which ball is the cue ball when you scratch?
comment: Usually, the cue ball is of slightly different diameter so it can be mechanically sorted out. In some machines, the cue ball is the same size but has a metal core that trips a magnetic field sensor and electronically triggers some kind of separating device.
passages: The balls range from in diameter to in diameter. Under the WPA/BCA "(see below)" equipment specifications, the weight may be from 5.5 to 6 oz. (156–170 g) with a diameter of 2.25 in. (57.15 mm), plus or minus 0.005 in. (0.127 mm). Modern coin-operated pool tables generally use one of three methods to distinguish and return the cue ball to the front of the table while the numbered balls return to an inaccessible receptacle until paid for again: the cue ball is larger and heavier than the other balls, or denser and heavier, or has a magnetic core. 
   As with other entries in the Virtual Pool series, the game is controlled by keyboard and mouse. Shots are made by holding down specific keyboard buttons, whilst moving the mouse backwards and then forwards to mimic stroking the . The speed at which the mouse is moved forwards determines the strength of the shot being played.
   As COPS, above, but the calibration of the software to detect ball presence is automatic. Note also that Sensi incorporates an LDS (Load Detection System) that allows it to detect presence of balls further up the stack, occasionally allowing exceedingly-fast performance when it detects a full, pressured stack.
  
  Section::::Ball detection systems.:Weight sensor.:Noise activated.
   Section::::Draw.
  
  Draw, sometimes called back-spin or "bottom," is backward spin applied to the cue ball by hitting it below the midpoint of its vertical plane as it faces the shooter. If the cue ball is hit with draw, and if that spin remains on the cue ball at the moment of impact with an object ball, the cue ball will reverse direction on a dead-on or center-to-center hit, and "draw" backwards. Draw is referred to in the United Kingdom as "screw" or "back-spin".
   Section::::Shaft.:Tip.
  
  Leather tips of varying curvature and degrees of hardness are glued to (or in some cases screwed into) the ferrule. The "de facto" standard curvatures for a pool tip are dime- and nickel-radius, determined by shaping a tip so that when one puts a nickel or dime to it, they have the same curvature. The tip end of the cue will vary in diameter but is typically in the 9 to 14 millimeter range with 12–13 mm for pool cues, and 9–10 mm for Snooker cues being most common.
   Section::::Game types.:Racked games.:Rotation games.
   The primary rule of the game is that the "lowest numbered" object ball on the table at any time is the "" and must be struck first (including on the break shot – a side break is a foul), regardless of the player's intentions of which ball to actually pocket. Players may use the lowest numbered ball to pocket other (e.g. higher value) balls. Consequently, this not being a game, points are also counted if a ball is unintentionally but legally pocketed (a "" or ""). A player's turn at the table continues until a shot fails to legally pocket a ball, a foul is committed, or the frame concludes. Illegally pocketed balls are spotted.
   If the cue ball hits an object ball at an angle and has follow on it (is spinning forward), the cue ball will first travel on the tangent line and then parabolically arc forward from the tangent line in the direction of cue ball travel. By the same token, when such impact is made and the cue ball has draw (back-spin) on it, the cue ball will first travel on the tangent line and then parabolically arc backward from the tangent line in the opposite direction of cue ball travel. Whether follow or draw is on the cue ball, the faster the cue ball is traveling at the moment of impact, the farther it will travel on the tangent line before arcing forward or backward.
   Draw applied to a non-dead-on shot will cause the angle of departure of the cue ball from the object ball to narrow shortly after impact. Similarly, it will cause a narrowing of the cue ball's rebound angle after impact with a rail cushion.
  
  Draw can also be used to slow the rate of cue ball travel as a result of increased friction between the cloth and the cue ball. This is often called "drag draw".
   Top spin is imparted to a ball by hitting it above the midpoint of its vertical plane as it faces the shooter. Top spin is spin in the direction a ball naturally "wants" to take in reaction to friction from contact with the pool cloth. Because of this, a ball sliding on the cloth will rapidly pick up follow. Likewise, a ball struck so that it is spinning backwards (with "draw" — see below) immediately starts losing that spin, and if it travels far enough, will reach a sliding point (no spin), soon graduating to natural follow.
   Normal ball and rail foul rules apply in cribbage. This is a requirement present in most pool games that a player must contact an with the cue ball and after that contact, either pocket an object ball, or some ball including the cue ball must contact a rail. When a foul results from the cue ball into a pocket or jumping it off the table, the player has cue ball in hand from the kitchen. When a player has cue ball in hand from the kitchen and all object balls are also behind the head string in the , a player has the option of having the object ball nearest the head string relocated to the foot spot. If in this situation two or more object balls are equidistantly closest to the head string, the player may designate which ball is to be relocated.
   If a cue ball is sliding, not rolling, at the time it contacts an object ball at an angle (i.e. on a , a center-to-center impact), the cue ball will travel in a line tangential to the point of impact between both balls – the . Because billiard balls are somewhat elastic, the resulting tangent line is slightly less than 90 degrees from perpendicular to a line formed by the contact point between the balls.
   Coin-operated pool tables such as those found at bars historically have often used either an oversized cue, larger than the more popular magnetic cue. Sometimes the cue can be a less expensive type of ball refereed to as a mud ball. Which is a ball with metal grindings mixed into the resin, so much it is magnetic enough to separate, like a metal core ball! Unlike the regular set of balls (which are captured until the game ends and the table is paid again for another game) as it makes it possible that the cue ball can be returned for further play, should it be accidentally potted.) Oversized, I have seen, but not used in my area much. Where a regular coin op cue ball has a metal core in it. The oversize ball is separated by its size. A magnetic ball is separated by a magnet! In Asia and Europe, some pool tables use a smaller cue ball instead. Modern tables usually employ a magnetic ball of regulation or near-regulation size and weight, since players have complained for many decades that the heavy and often oversized cue balls do not "play" correctly.
   "" refers to a cue ball that is sliding across the cloth with no follow or draw spin. To illustrate this principle, if a ball was marked with a single red dot on it which faced the ceiling at the time the cue ball was struck, an observer would see the cue ball traveling with that red dot remaining fixed at the top of the ball, because the bottom of the ball is sliding over the cloth.
   In order to initially achieve a sliding cue ball, a middle-ball hit is employed. The more speed with which the cue ball is hit in this manner, the longer the cue ball will slide before picking up natural forward roll from cloth friction. However, because of this tendency of the cue ball to acquire follow from friction, in order to deliver a sliding cue ball to an object ball at a distance, the cue ball must be precisely hit with the necessary degree of draw so that by the time it reaches the object ball, the draw has dissipated and the cue ball is sliding at the moment of impact.
   Another variation (regardless of the above spotting rule) that is common in North America is that the incoming player after a scratch receives cue ball in-hand behind the () only, not in-hand anywhere on the table.
  
  Section::::Variations.:More players.
  
  Team play can be pairs (or more) of players being assigned to each of the three sets of balls and taking alternating turns or (in format) alternating shots during their turn.
   Fouls, in common bar pool, that are not cue-ball scratches generally only cause loss of turn, with cue ball left in place (even if it is ed). Even in the case of a scratch, this only results in . Regionally, there is a great deal of bar pool variation in the handling of fouls while shooting at or pocketing the 8 ball. In some cases any foul while shooting at but not pocketing the 8 is a loss of game, in others only a foul while otherwise successfully pocketing the 8, and in yet others only certain fouls, such as also sinking an opponent's ball and the 8 ball on the same shot, or hitting the 8 then cue-ball scratching, are game-losing.
   When played on coin-operated tables (such that balls cannot be returned to play at will once pocketed, only after paying for another game) a player who scratches selects one of his or her own balls to be pocketed immediately, in lieu of opponents' balls returning to the table. In the event that a scratch occurs on the same shot that an opponent's ball is pocketed, the affected opponent is permitted to select a ball belonging to the offender which is to be removed instead of the player that scratched choosing the ball to be pocketed. In either case, this can result in the scratching player being "out".
   Section::::Types.:Speciality.
  
  Manufacturers also provide a variety of specialty cues tailored to specific shots. Pool "break cues" have tips made from very hard leather (sometimes layered) or phenolic resin to ensure that the full force of the stroke is transferred to the cue ball during the , and to avoid excessive wear-and-tear on the tips and ferrules of players' main shooting cues. Phenolic-tipped break cues often have a merged phenolic ferrule-tip, instead of two separate pieces.
   The Wii Remote will act as the cue and players will be able to use it to set the power and the direction buttons to set the direction of the shot. However, the game does come with the option for players to set the strength of the shot by simply pressing buttons on the controller.
  
  Section::::Reception.
   The end of the cue is of larger circumference and is intended to be gripped by a player's hand. The of the cue is of smaller circumference, usually tapering to an terminus called a (usually made of fiberglass or brass in better cues), where a rounded leather is affixed, flush with the ferrule, to make final contact with balls. The tip, in conjunction with chalk, can be used to impart spin to the cue ball when it is not hit in its center.
   On the Wii, the game is controlled using the Wii Remote. Players aim their shot using either the pointer function of the Remote or the D-pad, with players miming the motion of a cue stick to hit the ball. Players can also can pinpoint the precise point on their cue ball they will strike with their cue stick to add spin and to pull off trick shots.
  
  Section::::Reception.
   This effect is sometimes overarchingly referred to as "the gear system;" so-called because the interaction of the cogwork gears of a clock — each circular gear is interlocked with an abutting circular gear and each spins in the opposite direction of its neighbor in a series. on the cue ball can cause a very similar effect. If the cue ball with left hand in the preceding scenario contacts an object ball relatively full and that object ball is frozen to another, the first object ball is thrown to the right and the second to the left, exactly as the name implies.
   Each table has different playable "locations", which determine which Pokémon are available for capture. A subset of available locations are displayed slot-machine style in the beginning of a game, and pressing A will select a starting location and launch the first ball into play. After that, each table has its own mechanism for advancing to the next location, including the locations not available at the start of the game.
   Section::::Throw.
  
  "" refers to an object ball's motion away from the impact line due to relative sideways sliding motion between the cue ball and object ball caused by sidespin or a cut angle.
  
  When a ball with (sidespin) on it hits an object ball with a degree of fullness, the object ball will be "thrown" in the opposite direction of the side of the cue ball the was applied. Thus, a cue ball with left hand on it will "throw" a hit object ball to the right. 
  
raw_presuppositions: Cue ball is the same as others so it should be undetectable by pool table. Cue ball is the same as others so it should be undetectable by pool table.
raw_corrections: Cue ball is slightly different diameter so it can be sorted out. Cue ball is slightly different diameter so it can be sorted out. 