Spear-thrower

A spear-thrower, spear-throwing lever, or atlatl is a tool that uses leverage to achieve greater velocity in dart or javelin throwing, and includes a bearing surface that allows the user to store energy during the throw. It may consist of a shaft with a cup or a spur at the end that supports and propels the butt of the spear. It is usually about as long as the user's arm or forearm. The user holds the spear-thrower in one hand, gripping near the end farthest from the cup. The user puts the butt end of the spear, or dart, in the cup, or grabs the spur with the end of the spear. The spear is much longer than the thrower. The user holds the thrower at the grip end, with the spear resting on the thrower and the butt end of the spear resting in the thrower's cup. The user can hold the spear, with the index and thumb, with the same hand as the thrower, with the other fingers. The user reaches back with the spear pointed at the target. Then the user makes an overhand throwing motion with the thrower while letting go of the spear with the fingers. The spear is thrown by the action of the upper arm and wrist. The throwing arm together with the atlatl acts as a lever. The spear-thrower is a low-mass, fast-moving extension of the throwing arm, increasing the length of the lever. This extra length allows the thrower to impart force to the dart over a longer distance, thus imparting more energy and higher speeds. Common modern ball throwers (such as lacrosse sticks, the cestas used in jai alai, and molded plastic arms used for throwing tennis balls for dogs to fetch) use the same principle. A spear-thrower is a...