What is a projectile in ballistics?

In ballistics, a projectile is any object propelled by force, whose motion and impact are studied within the science of ballistics. Ballistics is divided into internal, external, intermediate, and terminal ballistics, with each discipline dealing with a different aspect of a projectile's propulsion, flight, and impact. Internal ballistics concerns the projectile's propulsion, while external ballistics studies its flight. The transition between these stages is intermediate ballistics. Terminal ballistics studies the projectile's impact, including the wounding of personnel. Examples of projectiles include bullets, shells, and other missiles launched from firearms or artillery.

How does a projectile move through the air?

Ballistics is the science of how projectiles move, fly, and hit targets. When a projectile is fired, the hot gases produced by the propellant cause pressure to rise within the gun chamber. Once this pressure overcomes the projectile's resistance, it begins to move, accelerating to high speeds before exiting the muzzle. After leaving the gun, the projectile's path, or trajectory, is affected by gravity, drag, and lift. Without drag, the trajectory would be a parabola . Drag slows the projectile, especially at speeds below the speed of sound, where it is proportional to the square of the velocity. Factors such as tail fins and spin stabilization are used to stabilize projectiles.

What forces affect the flight of a projectile?

Ballistics is the science of how projectiles move in flight. Several forces affect a projectile's flight, including gravity, drag, and lift.

What is the difference between the path of a thrown ball and a fired bullet?

The path of a thrown ball and a fired bullet both represent projectile motion, but key differences arise from their initial velocities and the forces acting upon them. A thrown ball follows a parabolic path due to its lower initial velocity and significant air resistance. Gravity and air resistance quickly affect its trajectory, limiting its range and causing noticeable curvature. In contrast, a fired bullet boasts a far greater initial velocity. Over shorter distances, its path appears straighter because the effects of gravity and air resistance are less immediately apparent. However, as distance increases, the bullet's trajectory also curves downward due to gravity, and air resistance plays a crucial role in slowing it down.

How does gravity influence a projectile’s path?

Gravity is the primary force shaping a projectile's path, causing it to curve downwards from its initial trajectory. Projectile motion combines vertical free fall due to gravity and horizontal inertial motion. The vertical position ( z ) of the projectile changes according to the equation ( z = z_0 - \frac{1}{2}gt^2 ), where ( z_0 ) is the initial height, ( g ) is the acceleration due to gravity, and ( t ) is the time. The horizontal motion follows ( x(t) = v_x t ), where ( v_x ) is the constant horizontal speed. Combining these gives the projectile's trajectory as a parabola: ( z = z_0 - \frac{1}{2} g (\frac{1}{v_x})^2 x^2 ). Air resistance and other factors are ignored in this simplified model. The calculations are most accurate for heavy, slow-moving objects.

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Key People:: Sir Andrew Noble, 1st Baronet; Niccolò Fontana Tartaglia; Gregory Breit; Gilbert Ames Bliss

Related Topics:: projectile motion; intermediate ballistics; internal ballistics; external ballistics; gunnery

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What is a projectile in ballistics?
In ballistics, a projectile is any object propelled by force, whose motion and impact are studied within the science of ballistics. Ballistics is divided into internal, external, intermediate, and terminal ballistics, with each discipline dealing with a different aspect of a projectile's propulsion, flight, and impact.

Internal ballistics concerns the projectile's propulsion, while external ballistics studies its flight. The transition between these stages is intermediate ballistics. Terminal ballistics studies the projectile's impact, including the wounding of personnel. Examples of projectiles include bullets, shells, and other missiles launched from firearms or artillery.
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How does a projectile move through the air?
Ballistics is the science of how projectiles move, fly, and hit targets. When a projectile is fired, the hot gases produced by the propellant cause pressure to rise within the gun chamber. Once this pressure overcomes the projectile's resistance, it begins to move, accelerating to high speeds before exiting the muzzle.

After leaving the gun, the projectile's path, or trajectory, is affected by gravity, drag, and lift. Without drag, the trajectory would be a parabola. Drag slows the projectile, especially at speeds below the speed of sound, where it is proportional to the square of the velocity. Factors such as tail fins and spin stabilization are used to stabilize projectiles.
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2. mechanics: Projectile motion
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What forces affect the flight of a projectile?
Ballistics is the science of how projectiles move in flight. Several forces affect a projectile's flight, including gravity, drag, and lift.
- Gravity causes a projectile to follow a curved, parabolic path.
- Drag is air resistance that slows the projectile's motion along its trajectory. Drag is related to the projectile's velocity squared. Projectiles with a more streamlined shape experience less drag.
- Lift is an aerodynamic force. The spinning of a projectile can generate lift (the Magnus effect), causing the projectile to swerve.
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What is the difference between the path of a thrown ball and a fired bullet?
The path of a thrown ball and a fired bullet both represent projectile motion, but key differences arise from their initial velocities and the forces acting upon them. A thrown ball follows a parabolic path due to its lower initial velocity and significant air resistance. Gravity and air resistance quickly affect its trajectory, limiting its range and causing noticeable curvature.

In contrast, a fired bullet boasts a far greater initial velocity. Over shorter distances, its path appears straighter because the effects of gravity and air resistance are less immediately apparent. However, as distance increases, the bullet's trajectory also curves downward due to gravity, and air resistance plays a crucial role in slowing it down.
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2. mechanics: Projectile motion
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How does gravity influence a projectile’s path?
Gravity is the primary force shaping a projectile's path, causing it to curve downwards from its initial trajectory. Projectile motion combines vertical free fall due to gravity and horizontal inertial motion. The vertical position ( z ) of the projectile changes according to the equation ( z = z_0 - \frac{1}{2}gt^2 ), where ( z_0 ) is the initial height, ( g ) is the acceleration due to gravity, and ( t ) is the time.

The horizontal motion follows ( x(t) = v_x t ), where ( v_x ) is the constant horizontal speed. Combining these gives the projectile's trajectory as a parabola: ( z = z_0 - \frac{1}{2} g (\frac{1}{v_x})^2 x^2 ).

Air resistance and other factors are ignored in this simplified model. The calculations are most accurate for heavy, slow-moving objects.
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1. mechanics: Projectile motion
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ballistics, science of the propulsion, flight, and impact of projectiles. It is divided into several disciplines. Internal and external ballistics, respectively, deal with the propulsion and the flight of projectiles. The transition between these two regimes is called intermediate ballistics. Terminal ballistics concerns the impact of projectiles; a separate category encompasses the wounding of personnel.

The gun and the rocket motor are types of heat engine, partially converting the chemical energy of a propellant into the kinetic energy of a projectile. Propellants are unlike conventional fuels in that their combustion does not require atmospheric oxygen. Within a restricted volume, the production of hot gases by a burning propellant causes an increase in pressure. The pressure propels the projectile and increases the burning rate. The hot gases tend to erode the gun bore or rocket throat.

When the charge of propellant in a gun chamber is ignited, the combustion gases are restrained by the shot, so the pressure rises. The shot starts to move when the pressure on it overcomes its resistance to motion. The pressure continues to rise for a time and then falls, while the shot is accelerated to a high velocity. The rapidly burning propellant is soon exhausted, and, in time, the shot is ejected from the muzzle: muzzle velocities up to 15 kilometres (9 miles) per second have been achieved. Recoilless guns vent gas through the rear of the chamber to counteract recoil forces.

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A precursor blast, which precedes the exit of the shot, is followed by the main blast as the compressed gases behind the shot are released. The shot is briefly overtaken by the rapid gas outflow and so may suffer severe yawing. The blast shock wave, traveling outward at a speed greater than that of sound, is heard as gunfire. Heat generated near the muzzle causes flash, which in large guns is accompanied by flames. Devices can be affixed to the muzzle to suppress blast and flash by dispersing shock waves, and they can reduce recoil by deflecting the outflow.

A trajectory is the path of a shot, subject to the forces of gravity, drag, and lift. Under the sole influence of gravity, a trajectory is parabolic. Drag retards motion along the trajectory. Below the speed of sound, the drag is roughly proportional to the square of the velocity; streamlining of the shot tail is effective only at these velocities. At greater velocities, a conical shock wave emanates from the nose of the shot. The drag, which is largely dependent on the nose shape, is least for finely pointed shots. Drag can be reduced by venting gases from a burner in the tail.

Tail fins can be used to stabilize projectiles. Spin stabilization, provided by rifling, causes gyroscopic wobbling in response to aerodynamic tumbling forces. Insufficient spin permits tumbling, and too much prevents dipping of the shot nose as it traverses the trajectory. Drift of the shot arises from lift, due to yawing, meteorological conditions, and rotation of the Earth.

Rockets are propelled by reaction to the momentum of the gas efflux. The motor is designed so that the pressures generated are nearly constant during burning. Fin-stabilized rockets are sensitive to crosswinds, as resulting yaw causes thrust misalignment. Two or more motor nozzles canted from the line of flight can provide spin stabilization.

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Targets are generally solid and are termed thick or thin according to whether or not the impact of the shot is influenced by underlying material. Penetration occurs when the stress intensities of impact exceed the yield stress of the target; it causes ductile and brittle failure in thin targets and hydrodynamic flow of material in thick targets. The shot may be subject to similar failure during impact. Penetration completely through the target is called perforation. Enhanced armour penetrators either detonate a squashed explosive against the target or explosively focus a jet of metal onto its surface.

Wound ballistics is mainly concerned with the mechanisms and medical implications of trauma caused by bullets and explosively driven fragments. Upon penetration, the momentum given to the surrounding tissues generates a large temporary cavity. The extent of local injury is related to the size of this transient cavity. Evidence suggests that physical injury is proportional to the projectile’s velocity cubed, its mass, and its cross-sectional area. The wounding potential of a bullet is thus increased by tumbling or mushrooming upon impact. Further injury is often caused by fast-moving fragments of impacted bone. Studies of body armour seek to prevent projectile penetration and minimize injury.

This article was most recently revised and updated by John P. Rafferty.

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