Hockey puck
Appearance
A puck is a hard rubber disk used in ice hockey, about one inch high and 3 inches in diameter. It is frozen a few hours before the game to prevent bouncing. Pucks can reach speed of 100 miles per hour when hit by players' sticks, and spectators at hockey games are occasionally injured. On March 18, 2002, a teenage girl was killed by a hockey puck at an NHL game (source)