The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Zitzewitz, Paul W. & Robert F Neff. Physics: Principles and Problems. New York: Glance, 1995: 84.||"If a bullet leaves the muzzle of a rifle with a speed of 600 m/s, and the barrel of the rifle is 0.9 m long, what is the acceleration of the bullet while in the barrel?"||2.0 × 105 m/s2|
|Badness, Frank C. & M.L. McPherson. Cartridges of the World: 9th Edition. Iola, WI: Krause Publications, 2000.||"7.21 Firebird Factory Ballistics (27 inch barrel) … Velocity: 3950 [fps]"||1.1 × 106 m/s2|
|Myatt, Frederick. An Illustrated Guide to Pistols and Revolvers. London, United Kingdom: Salamander House, 1981.||"Beretta Model 92S–9 mm … Barrel: 5" (127 mm) … Muz Vel: 335 m/s"||4.4 × 105 m/s2|
|Popenker, Max R. Fabrique Nationale (FN) Five-seveN (Belgium). Modern Firearms & Ammunition. 2000.||"Barrel length: 122.5 mm … The SS190 ammunition looks like a scaled down 5.56 mm NATO round and boosts the 2.02 gram (31 grains) pointed steel and aluminum core bullet to the muzzle velocity of 650 meters per second from the pistol barrel."||1.7 × 106 m/s2|
Bullets are cylindrical metal projectiles shot from firearms. Their main function is to kill or otherwise incapacitate. They come in numerous varieties for use in handguns, rifles, and machine guns. There is also special ammunition capable of penetrating armor, firing underwater, or firing "silently" at subsonic speeds. However, their designs are all basically the same. A typical cartridge consists of four components: the cartridge case, primer, propellant charge and bullet. When a gun trigger is pulled, the primer is struck, igniting the propellant. This causes a rapid expansion of gas, which forces the bullet forward and ejects the casing. Contrary to popular belief, guns are not loaded with bullets, but cartridges, and they fire bullets (since bullets are a more common term and the actual objects responsible for harm, they receive the recognition).
While small in size (the most popular handgun bullet is 9 mm in diameter) bullets posses enough kinetic energy to cause serious damage. Using a kinematics formula, it is possible to determine the acceleration of a bullet when the muzzle velocity and barrel length of a gun are known.
v2 = vo2 + 2as
v is the muzzle velocity
vo is the initial velocity of the bullet, which is zero
a is the acceleration
s is the barrel length
Since acceleration is the desired value, the derived formula is this:
When fired from a Beretta 92S, the standard issue US Army pistol, a 9 mm Parabellum bullet has a muzzle velocity of 335 m/s. With its 127 mm barrel length, the bullet's acceleration is calculated to be 4.4 × 105 m/s2.
The acceleration of a bullet depends largely on the gun from which it is fired, along with the intent of the user. Pistol bullets generally feature a lower acceleration than rifles or machine guns. Also, individuals involved with clandestine operations may use firearms with silencers, which suppress bullet speed and require special subsonic ammunition.
Remember, guns don't kill people. Bullets do. To paraphrase Chris Rock in Bigger, Blacker and Uncut, if bullet prices were raised to $5,000 each, there would be a drastic decrease in murders [mp3].
Michael Tse -- 2003
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