A projectile is any object propelled through space by the exertion of a force which ceases after launch. Although a thrown baseball could be considered a projectile, the word more often refers to a weapon. For details of the mathematics surrounding projectile trajectory, see equations of motion.
Arrows, darts, spears, and similar weapons are fired using pure mechanical force applied by another solid 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.
Some projectiles provide propulsion during (part of) the 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": an ICBM is a missile with rocket engines.
Many projectiles, e.g. shells, contain an explosive charge. With or without explosive charge a projectile can be designed to cause special damage, e.g. fire (see also early thermal weapons), or poisoning (see also arrow poison).
See also: KE-Munitions
Projectiles which do not contain an explosive charge are termed kinetic projectile, kinetic energy weapon, kinetic warhead or kinetic penetrator. Classic kinetic energy weapons are blunt projectiles such as rocks and round shot, 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 objective, 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 they need to attain a high velocity anyway, they can destroy their target with their released kinetic energy alone; explosives are not necessary. Compare the energy of TNT, 4.6 MJ/kg, to the energy of a kinetic kill vehicle with a closing speed of 10 km/s, which is 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.
With regard to anti-missile weapons, the Arrow missile and MIM-104 Patriot have explosives, but the Kinetic Energy Interceptor (KEI), Lightweight Exo-Atmospheric Projectile (LEAP, see RIM-161 Standard Missile 3), and THAAD being developed 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 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).
Some projectiles stay connected by a cable to the launch equipment after launching it:
|Projectile||Speed (m/s),(km/h)||(ft/s)||(mph)||Kinetic energy density = Speed^2 / 2|
|object falling 1 m||4.43 m/s, 15.948 km/h||14.5 ft/s||9.9 mph||9.8 J/kg|
|object falling 10 m||14 m/s, 50.4 km/h||46 ft/s||31 mph||98 J/kg|
|thrown club (weapon) (expert thrower)||40 m/s, 144 km/h||130 ft/s||90 mph||800 J/kg|
|object falling 100 m||45 m/s, 162 km/h||150 ft/s||100 mph||980 J/kg|
|refined (= flexible) atlatl dart (expert thrower)||45 m/s, 162 km/h||150 ft/s||100 mph||1000 J/kg|
|80-lb-draw pistol crossbow bolt||58 m/s, 208.8 km/h||190 ft/s||130 mph||1.7 kJ/kg|
|paintball fired from marker||91 m/s, 327.6 km/h||300 ft/s||204 mph||4.1 kJ/kg|
|175-lb-draw crossbow bolt||97 m/s, 349.2 km/h||320 ft/s||217 mph||4.7 kJ/kg|
|air gun pellet 6 mm BB||100 m/s, 360 km/h||328 ft/s||224 mph||5 kJ/kg|
|rifle bullet 4.5 mm||150 m/s, 540 km/h||492 ft/s||336 mph||11 kJ/kg|
|air gun pellet (conventional maximum)||244 m/s, 878.4 km/h||800 ft/s||545 mph||29.8 kJ/kg|
|9x19 mm (bullet of a pistol)||340 m/s, 1224 km/h||1116 ft/s||761 mph||58 kJ/kg|
|12.7x99 mm (bullet of a heavy machine gun)||800 m/s, 2880 km/h||2625 ft/s||1790 mph||320 kJ/kg|
|5.56x45 mm (standard bullet used in many assault rifles)||920 m/s, 3312 km/h||3018 ft/s||2058 mph||470 kJ/kg|
|125x1400 mm (shell of a tank)||1700 m/s, 6120 km/h||5577 ft/s||3803 mph||1.4 MJ/kg|
|2kg Tungsten Slug (from Experimental Railgun)||3000 m/s, 10800 km/h||9843 ft/s||6711 mph||4.5 MJ/kg|
|ICBM reentry vehicle||up to 4 km/s||up to 13000 ft/s||up to 9000 mph||up to 8 MJ/kg|
|projectile of a light gas gun||up to 7 km/s||up to 23000 ft/s||up to 16000 mph||up to 24 MJ/kg|
|satellite in low earth orbit||8 km/s||26000 ft/s||19000 mph||32 MJ/kg|
|Exoatmospheric Kill Vehicle||closing speed roughly 10 km/s||~33000 ft/s||~22000 mph||~ 50 MJ/kg|
|projectile (e.g. space debris) and target both in low earth orbit||closing speed 0 - 16 km/s||~53000 ft/s||~36000 mph||~ 130 MJ/kg|
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.
Projectile is also the name of an annual anarchist film festival based in Newcastle UK * 
Projectile weapons have been used for a long time. Bows and slingshots are very old weapons that were used hundreds of years ago. Now most countries use projectile weapons instead of melee weapons like swords. This is because modern projectile weapons such as guns, rocket launchers, and artillery cannons can shoot at long ranges and are usually more deadly than melee weapons.
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