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A projectile is any object projected into space (empty or not) by the exertion of a force. Although any object in motion through space (for example a thrown baseball) may be referred to as a projectile, the term more commonly refers to a ranged weapon. Mathematical equations of motion are used to analyze projectile trajectory.

Motive force

Arrows, darts, spears, and similar weapons are fired using pure mechanical force applied by another object; apart from throwing without tools, mechanisms include the catapult, slingshot, and bow.

Other weapons use the compression or expansion of gases as their motive force.

Blowguns and pneumatic rifles use compressed gases, while most other guns and firearms utilize expanding gases liberated by sudden chemical reactions. Light gas guns use a combination of these mechanisms.

Railguns utilize electromagnetic fields to provide a constant acceleration along the entire length of the device, greatly increasing the muzzle velocity.

Some projectiles provide propulsion during flight by means of a rocket engine or jet engine. In military terminology, a rocket is unguided, while a missile is guided. Note the two meanings of "rocket" (weapon and engine): an ICBM is a missile with rocket engines.

Ballistics analyze the projectile trajectory, the forces acting upon the projectile, and the impact that a projectile has on a target.

An explosion, whether or not by a weapon, causes the debris to act as multiple high velocity projectiles. An explosive weapon, or device may also be designed to produce many high velocity projectiles by the break-up of its casing, these are correctly termed fragments.

Delivery projectiles

Many projectiles, e.g. shells, may carry an explosive charge or another chemical or biological substance. Aside from explosive payload, a projectile can be designed to cause special damage, e.g. fire (see also early thermal weapons), or poisoning (see also arrow poison).

Kinetic projectiles

A projectile which does not contain an explosive charge or any other kind of charge is termed a kinetic projectile, kinetic energy weapon, kinetic energy warhead, kinetic warhead or kinetic penetrator. Typical kinetic energy weapons are blunt projectiles such as rocks and round shots, pointed ones such as arrows, and somewhat pointed ones such as bullets. Among projectiles which do not contain explosives are those launched from railguns, coilguns, and mass drivers, as well as kinetic energy penetrators. All of these weapons work by attaining a high muzzle velocity (hypervelocity), and collide with their target, converting their kinetic energy into destructive shock waves and heat.

Some kinetic weapons for targeting objects in spaceflight are anti-satellite weapons and anti-ballistic missiles. Since in order to reach an object in orbit it is necessary to attain an extremely high velocity, their released kinetic energy alone is enough to destroy their target; explosives are not necessary. For example: the energy of TNT is 4.6 MJ/kg, and the energy of a kinetic kill vehicle with a closing speed of 10 km/s is of 50 MJ/kg. This saves costly weight and there is no detonation to be precisely timed. This method, however, requires direct contact with the target, which requires a more accurate trajectory. Some hit-to-kill warheads are additionally equipped with an explosive directional warhead to enhance the kill probability (e.g. Israeli Arrow missile or U.S. Patriot PAC-3).

With regard to anti-missile weapons, the Arrow missile and MIM-104 Patriot PAC-2 have explosives, while the Kinetic Energy Interceptor (KEI), Lightweight Exo-Atmospheric Projectile (LEAP, used in Aegis BMDS), and THAAD do not (see Missile Defense Agency).

A kinetic projectile can also be dropped from aircraft. This is applied by replacing the explosives of a regular bomb, e.g. by concrete, for a precision hit with less collateral damage. A typical bomb has a mass of 900 kg and a speed of impact of 800 km/h (220 m/s). It is also applied for training the act of dropping a bomb with explosives. This method has been used in Operation Iraqi Freedom and the subsequent military operations in Iraq by mating concrete-filled training bombs with JDAM GPS guidance kits, to attack vehicles and other relatively "soft" targets located too close to civilian structures for the use of conventional high explosive bombs.

A Prompt Global Strike may use a kinetic weapon. A kinetic bombardment may involve a projectile dropped from Earth orbit.

A hypothetical kinetic weapon that travels at a significant fraction of the speed of light, usually found in science fiction, is termed a relativistic kill vehicle (RKV).

Wired projectiles

Some projectiles stay connected by a cable to the launch equipment after launching it:

• for guidance: wire-guided missile (range up to 4,000 meters)
• to administer an electric shock, as in the case of a Taser (range up to 10.6 meters); two projectiles are shot simultaneously, each with a cable.
• to make a connection with the target, either to tow it towards the launcher, as with a whaling harpoon, or to draw the launcher to the target, as a grappling hook does.

Typical projectile speeds

See also

• Atlatl
• Ballistics
• Gunpowder
• Impact depth
• Kinetic bombardment
• Projectile point
• Projectile use by living systems
  • Arrow
  • Dart
  • Missile
  • Sling ammunition
  • Spear
  • Torpedo
• Range of a projectile
• Space debris
• Toypedo
• Trajectory of a projectile

References

1. "The free Dictionary". Retrieved 2010-05-19.
2. "Dictionary.com". Retrieved 2010-05-19.

External links

• Open Source Physics computer model
• Projectile Motion Applet
• Another projectile Motion Applet

• Projectiles
• Ammunition
• Ballistics