A projectile is any object thrown by the exertion of a
force. It can also be defined as an object launched into the space and allowed to move free under the influence of gravity and air resistance. Although any object in motion through
space (for example a thrown
baseball, kicked football, fired bullet, thrown arrow, stone released from catapult) may be called projectiles, they are commonly found in warfare and sports. Mathematical
equations of motion are used to analyze projectile
trajectories.
Motive force
Blowguns and
pneumatic rifles use compressed gases, while most other
guns and
cannons utilize expanding gases liberated by sudden chemical reactions by
propellants like
smokeless powder.
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 guided missile with a rocket engine.
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).
Sport projectiles
thumb|Ball speeds of have been recorded in baseball.
In projectile motion the most important force applied to the ‘projectile’ is the propelling force, in this case the propelling forces are the muscles that act upon the ball to make it move, and the stronger the force applied, the more propelling force, which means the projectile (the ball) will travel farther. See
pitching,
bowling.
Kinetic projectiles
A projectile that does not contain an explosive charge or any other kind of payload is termed a ''kinetic projectile'', ''kinetic energy weapon'', ''kinetic energy warhead'', ''kinetic warhead'', ''kinetic kill vehicle'' 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 that 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, or initial velocity, generally up to
hypervelocity, and
collide with their targets, converting the
kinetic energy associated with the relative velocity between the two objects into destructive shock waves and heat. Other types of kinetic weapons are accelerated over time by a rocket engine, or by gravity. In either case, it is this kinetic energy that destroys its target.
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 is 50 MJ/kg. For comparison, 50MJ is equivalent to the kinetic energy of a
school bus weighing 5 metric tons, traveling at .
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 with a non-explosive material (e.g. concrete), for a precision hit with less
collateral damage. A typical bomb has a mass of and a speed of impact of . 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 )
* to administer an electric shock, as in the case of a
Taser (range up to ); 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.
*
Bolo shotgun ammunition
Typical projectile speeds
Equations of motion
An object projected at an angle to the horizontal has both the vertical and horizontal components of velocity. The vertical component of the velocity on the y-axis is given as
while the horizontal component of the velocity is
. There are various calculations for projectiles at a specific angle
:
1. Time to reach maximum height. It is symbolized as (
), which is the time taken for the projectile to reach the maximum height from the plane of projection. Mathematically, it is given as
where
= acceleration due to gravity (app 9.81 m/s²),
= initial velocity (m/s) and
= angle made by the projectile with the horizontal axis.
2. Time of flight (
): this is the total time taken for the projectile to fall back to the same plane from which it was projected. Mathematically it is given as
.
3. Maximum Height (
): this is the maximum height attained by the projectile OR the maximum displacement on the vertical axis (y-axis) covered by the projectile. It is given as
.
4. Range (
): The Range of a projectile is the horizontal distance covered (on the x-axis) by the projectile. Mathematically,
. The Range is maximum when angle
= 45°, i.e.
.
See also
*
Atlatl
*
Ballistics
*
Gunpowder
*
Bullet
*
Impact depth
*
Kinetic bombardment
*
Shell (projectile)
*
Projectile point
*
Projectile use by animals
*
Arrow
*
Dart
*
Missile
*
Sling ammunition
*
Spear
*
Torpedo
*
Range of a projectile
*
Space debris
*
Trajectory of a projectile
Notes
References
*
External links
Open Source Physics computer modelProjectile Motion Applet
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Category:Ammunition
Category:Ballistics