Game Development Reference
In-Depth Information
When the projectile strikes the target, whether it bounces off the target or penetrates the
target, the momentum of the projectile changes because the target exerts a force on the bullet
and the bullet exerts an equal and opposite force on the target. This force, also known as
blunt
trauma
, can significantly damage a person wearing body armor even if the armor itself stops
the bullet. When programming a combat simulation, you might consider adding blunt trauma
to the damage calculation, making it some function of the projectile momentum at impact.
If you use damage meters in your shoot-em-up game, the damage level should increase for every
hit whether or not the projectile penetrates the armor of the target.
Force due to momentum change is also apparent when the bullet or other projectile is
fired. When the exploding charge propels the bullet forward, the momentum of the bullet
changes, indicating that a force is being applied to the bullet. An equal and opposite force is
applied to the gun. This force is the recoil that occurs when the gun is fired. The recoil force is
proportional to the momentum imparted to the bullet, which is why a heavier bullet such as
the 44 Magnum will have greater recoil force than a lighter bullet such as a 9
mm
. In fact, two
separate recoil events take place. The first recoil occurs when the bullet starts to move down
the muzzle, and a second recoil happens when the bullet leaves the muzzle into the
surrounding air.
The impact force of a bullet is often ridiculously overstated in movies and games where a
gunshot victim will be thrown backwards through a plate glass window or some such thing.
Because drag forces will slow the bullet down during its flight, the impact force at the target will
always be less than the initial recoil force. In your game programming simulations, if the recoil
doesn't knock the shooter over, the impact shouldn't knock the victim over.
Body Wounds
In game simulations where participants are being wounded by guns, arrows, or other projectiles,
you may want to model or display the wounds that the projectiles will cause. This section will
provide a brief discussion of what happens when a bullet passes through a person's body. The
intent is to provide you with the proper scenarios when you are creating the graphics to go with
shoot-em-up games.
■
Caution
Just as a warning, some of the material in this section will be a bit graphic. If you don't want to
add these kinds of effects to your games, you might be better off skipping down to “Heat Conduction.”
As a bullet passes through a human body, it transfers some of its kinetic energy to the
surrounding tissue, causing the tissue to move away perpendicularly from the path of the bullet.
The tissue movement causes a temporary cavity that can be significantly larger in diameter
than the diameter of the bullet. For low-velocity bullets, such as most handgun bullets, the
kinetic energy transfer is small enough so that only a small temporary cavity is produced. Most
of the damage caused by a low-velocity bullet is along the direct path of the bullet.
The situation is quite different and rather disturbing for high-velocity bullets such as the
7.62
mm
NATO FMJ. When a high-velocity bullet enters the body, injured tissue is ejected out
of the entrance wound in what is called a “tail splash.” A large amount of kinetic energy is
transferred to the surrounding tissue as the bullet passes through, causing a large temporary
