Spear-thrower

A spear-thrower, spear-throwing lever, or atlatl (pronounced /ˈætlætəl/ ^ⓘ or /ˈɑːtlɑːtəl/; Nahuatl ahtlatl Nahuatl pronunciation: [ˈaʔt͡ɬat͡ɬ]) 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's 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 they make an overhand throwing motion with the thrower while letting go of the spear with the fingers.

The dart 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 molded plastic arms used for throwing tennis balls for dogs to fetch) use the same principle.

A spear-thrower is a long-range weapon and can readily impart to a projectile speeds of over 150 km/h (93 mph).

Spear-throwers appear early in human history in several parts of the world, and have survived in use in traditional societies until the present day, as well as being revived in recent years for sporting purposes. In the United States, the Nahuatl word atlatl is often used for revived uses of spear-throwers (or the Mayan word hul'che); in Australia, the Dharug word woomera is used instead.

The ancient Greeks and Romans used a leather thong or loop, known as an ankule or amentum, as a spear-throwing device. The Swiss arrow is a weapon that works similarly to amentum.

Using replicas of spear-throwers known from the Basketmaker culture and the Basketmaker II era, and using darts of different weights, it has been found that the maximum exit velocity a historical spear-thrower can achieve is 72—108 km/h (45—67 mph). Measurement methods include radar guns, gun chronographs, and analysis of high speed films, to cross-check the results. For comparison, a 25 lbs self bow shoots arrows with a exit velocity of 129 km/h (80 mph), while a replica of a 45 lbs self bow from the Catawba tribe achieves speeds of 160 km/h (100 mph). Claims of higher speeds of 160 km/h (100 mph) or even higher for historical self-throwers are probably due to improper measurement methods for this class of weapon.

The momentum gained by a spear thrower's dart is 1.8–2.7 kg•m•s, while that of a Catawba bow's arrow is 1.5 kg•m•s. A .357 magnum round of 158 grain gains a momentum of 3.58 kg•m•s.