# Projectile

A projectile is any object propelled through space by the exertion of a force that ceases after launch. In a general sense, even a football or baseball may be considered a projectile. It can cause damage (injury, property damage) to a person, animal or object it hits, depending on factors including size, shape, speed and hardness. Accordingly, in practice most projectiles are designed as weapons.

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.

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 (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.

## Contents

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).

## Kinetic projectiles

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 also railguns, coilguns, mass drivers, and kinetic energy penetrators. All of these weapons work by attaining a high muzzle velocity (hypervelocity), and collide with their objective, releasing kinetic energy.

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 ten 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. In this approach, the explosives of a regular bomb may be replaced with concrete, for a precision hit that causes less collateral damage.[1] A typical bomb has a mass of 900 kg and an impact speed of 800 km/h (220 m/s). This method is also applied when training personnel in the act of dropping a bomb with explosives. It was 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 called 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 4000 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.

## Range of a projectile

The path of this projectile launched from a height y0 has a range d.

In physics, a projectile launched with specific initial conditions in a uniform gravity field will have a predictable range. This range can be calculated using the following parameters:

• g: the gravitational acceleration—usually taken to be 9.81 m/s2 near the Earth's surface
• θ: the angle at which the projectile is launched
• v: the velocity at which the projectile is launched
• y0: the initial height of the projectile
• d: the total horizontal distance travelled by the projectile

When neglecting air resistance, the range of a projectile will be

$d = \frac{v \cos \theta}{g} \left( v \sin \theta + \sqrt{(v \sin \theta)^2 + 2gy_0} \right)$

If (y0) is taken to be zero, meaning the object is being launched on flat ground, the range of the projectile will then simplify to

$d = \frac{v^2}{g} \sin 2 \theta$

## Typical projectile speeds

Projectile Speed (m/s) (ft/s) (mph) Kinetic energy
object falling 1 m 4.43 m/s 14.5 ft/s 9.9 mph 9.8 J/kg
object falling 10 m 14 m/s 46 ft/s 31 mph 98 J/kg
thrown club (weapon) (expert thrower) 40 m/s 130 ft/s 90 mph 800 J/kg
object falling 100 m 45 m/s 150 ft/s 100 mph 980 J/kg
refined (= flexible) atlatl dart (expert thrower) 45 m/s 150 ft/s 100 mph 1000 J/kg
80-lb-draw pistol crossbow bolt 58 m/s 190 ft/s 130 mph 1.7 kJ/kg
paintball fired from marker 91 m/s 300 ft/s 204 mph 4.1 kJ/kg
175-lb-draw crossbow bolt 97 m/s 320 ft/s 217 mph 4.7 kJ/kg
air gun pellet 6 mm BB 100 m/s 328 ft/s 224 mph 5 kJ/kg
rifle bullet 4.5 mm 150 m/s 492 ft/s 336 mph 11 kJ/kg
air gun pellet (conventional maximum) 244 m/s 800 ft/s 545 mph 29.8 kJ/kg
9x19 mm (bullet of a pistol) 340 m/s 1116 ft/s 761 mph 58 kJ/kg
12.7x99 mm (bullet of a heavy machine gun) 800 m/s 2625 ft/s 1790 mph 320 kJ/kg
5.56x45 mm (standard bullet used in many assault rifles) 920 m/s 3018 ft/s 2058 mph 470 kJ/kg
125x1400 mm (shell of a tank) 1700 m/s 5577 ft/s 3803 mph 1.4 MJ/kg
2kg Tungsten Slug (from Experimental Railgun) 3000 m/s 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 LEO 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 LEO closing speed 0 - 16 km/s ~53000 ft/s ~36000 mph ~ 130 MJ/kg

## Miscellaneous

Ballistics analyze 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 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.

The term projectile also refers to weapons or any other objects thrown, shot or otherwise directed to enemies in video games or computer games.

## Notes

1. Jim Randle (October 7, 1999), Concrete Bomb Correspondent Report, Pentagon. Retrieved January 14, 2009.

## References

• Crosby, Alfred W. 2002. Throwing Fire: Projectile Technology Through History. Cambridge: Cambridge University Press. ISBN 0521791588
• Hothem, Lar. 1983. Arrowheads & Projectile Points. Paducah, KY: Collector Books. ISBN 0891452281
• McCoy, Robert. 2004. Modern Exterior Ballistics: The Launch and Flight Dynamics of Symmetric Projectiles. Atglen, PA: Schiffer Pub. ISBN 0764307207

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