Tossing a coin

Penny flipping, coin tossing, or heads or tails is the practice of throwing a coin in the air and checking which side is showing when it lands to choose between two alternatives, sometimes to resolve a dispute between two parties. It is a form of sortition which inherently has only two possible and equally likely outcomes.

The historical origin of coin flipping is the interpretation of a chance outcome as the expression of divine will.

Coin flipping was known to the Romans as navia aut caput ("ship or head"), as some coins had a ship on one side and the head of the emperor on the other. In England, this was referred to as cross and pile. The expression Heads or Tails results from heads and tails being considered opposite body parts.

During a coin toss, the coin is thrown into the air such that it rotates edge-over-edge several times. Either beforehand or when the coin is in the air, an interested party calls "heads" or "tails", indicating which side of the coin that party is choosing. The other party is assigned the opposite side. Depending on custom, the coin may be caught; caught and inverted; or allowed to land on the ground. When the coin comes to rest, the toss is complete and the party who called correctly or was assigned the upper side is declared the winner.

It is possible for a coin to land on its edge, usually by landing up against an object (such as a shoe) or by getting stuck in the ground (as famously happened during the December 8, 2013 NFL match up between the Philadelphia Eagles and Detroit Lions, which took place during a heavy snowstorm). However, even on a flat surface it is possible for a coin to land on its edge, with a chance of about 1 in 6000 for an American nickel.Angular momentum typically prevents most coins from landing on their edges unsupported if flipped. Such cases in which a coin does land on its edge are exceptionally rare and in most cases the coin is simply re-flipped.

The coin may be any type as long as it has two distinct sides; it need not be a circulating coin as such. Larger coins tend to be more popular than smaller ones. Some high-profile coin tosses, such as the Cricket World Cup and the Super Bowl, use custom-made ceremonial medallions.

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