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A projectile is any object sent through the air by the application of some force. In a general sense, even a football or baseball may be considered a projectile, but in practical action most projectiles are designed as weapons.
Motive force
Arrows, darts, spears, and similar weapons are fired using pure mechanical force applied by another solid object; conversely, 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.
Railguns provide a constant acceleration along the entire length of the device, greatly increasing the muzzle velocity.
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.
Blunt or sharp Although blowguns use small darts, most types of guns and firearms hurl bullets, pellets, or shot made of a metal, usually lead, that are designed to deform and fragment inside a target, causing significant damage. Items like arrows, hand darts, and spears are generally tipped with sharp metallic or lithic artifacts called projectile points that allow them to more easily penetrate a target, although some types of arrows used for hunting are designed to stun or kill through shock rather than to penetrate.
Projectiles designed to be non-lethal, for example for use against riots, include rubber bullets and flexible baton rounds.
Explosive charge or kinetic Projectiles may or may not contain an explosive charge. Shells do, bullets do not. Without it the hit may be like a collision.
Not only light weapons have projectiles without explosives, but also some powerful weapons, with a very high muzzle velocity: a kinetic energy penetrator, railgun, mass driver.
Projectiles for targeting objects in spaceflight are anti-satellite weapons and anti-ballistic missiles. Since they need to have a large speed anyway, they can destroy without explosives; compare the energy value for TNT, 4.6 MJ/kg, with the energy of a kinetic kill vehicle with a closing speed of e.g. 10 km/s, which is 50 MJ/kg. This saves costly weight and there is no detonation to be done at the right time, but on the other hand it requires a more accurate hit. The Arrow missile and MIM-104 Patriot have explosives, but of the KEI, LEAP, and THAAD being developed, none has (see Missile Defense Agency).
See also hypervelocity terminal ballistics, EKV.
For a fictional kinetic weapon, see Relativistic kill vehicle.
Miscellaneous Ballistics analyses the projectile trajectory, the forces acting upon the projectile, and the impact that a projectile has on a target. A guided missile is not called a projectile.
An explosion, whether or not by a weapon, causes debris to act as projectiles. An explosive weapon may be designed to produce shrapnel.
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