# ballistics

Cannon elevated at 45 degrees above the horizon using the artillerist's quadrant.

Ballistics is the study of the dynamics of an object, or **projectile**,
moving solely under the influence of a gravitational
field. It is traditionally divided into three parts.

**Interior ballistics** is concerned with the progress of the
projectile before it is released from the launching device. In the case
of a gun this involves determining the propellant charge, barrel design,
and firing mechanism needed to give the desired muzzle velocity and stabilizing
spin to the projectile.

**External ballistics** is concerned with the free flight of
the projectile. At the beginning of the seventeenth century Galileo determined that the trajectory (flight
path) of a projectile should be parabolic,
as indeed it would be if the effects of air resistance, the rotation and
curvature of the Earth, the variation of air density and gravity with height,
and the rotational inertia of the projectile
could be ignored. The shock waves accompanying
projectiles moving faster than the speed
of sound are also the concern of this branch.

**Aeroballistics** is the study of the motion of bodies whose flight path is determined by applying the principles of both aerodynamics and ballistics to different portions of the path.

**Terminal** or **penetration ballistics** deals
with the behavior of projectiles on impacting at the end of their trajectory.
The velocity-to-mass ratio of the impact particle is an important factor
and results are of equal interest to the designers of ammunition and or
armor plate. A relatively recent development in the science is **forensic
ballistics**, which plays an important role in the investigation
of gun crimes.

## Ballistic coefficient

The ballistic coefficient is a measure of a projectile's ability to coast. It is defined as *C*_{b} = *M*/*C*_{d }*A* where *M* is the projectile's
mass and *C*_{d}* A* is the drag
form factor. At any given velocity and air density, the deceleration
of a rocket from drag is inversely proportional
to this value. Intuitively, it is the principle behind why a tightly crumpled
piece of paper can be thrown farther than a loosely crumpled one.