A corrupt business, Cyrez, is manufacturing a handheld rail gun which fires aluminum bullets at nearly the speed of light. Not being content merely with fat government contracts, Cyrez is going to sell the gun to the Russian mafia, but must first neutralize Lee Cullen (Vanessa Williams) who is spying on them for the FBI. So how do the wicked Cyrez assassins attempt to dispose of Lee? With the rail gun, of course, but not before John Kruger (Arnold Schwarzenegger) shows up to save her. This pretty much requires the rest of the movie to accomplish.

As Lee observes, "...they said the physics [of the rail gun] were impossible", and we're inclined to heartily agree. The first problem is a nasty little law of physics called conservation of momentum. Briefly, this states that the forward momentum of the bullet must be counteracted by the backward momentum of the gun. The magnitude of an object's momentum is equal to its mass times the magnitude of its velocity, as expressed by the following equation:

p = mv

We know that the bullet is travelling close to the speed of light (3 × 10⁸ m/s). To be conservative, we will assume the bullet travels at only half the speed of light, and that its mass is about the mass of a paper clip (0.0005 kg). For the sake of simplicity, we will ignore the effects of relativity, which would cause the bullet's mass to be even greater. Thus, we calculate the bullet's momentum:

If we assume the mass of the rifle is 10 kg, its backward velocity must be 7.5 × 10⁴ N·s divided by 10 kg, which equals 7500 m/s. Compared to the velocity of a .45 cal bullet going a sedate 330 m/s, our rail gun would be a mite difficult to hold.

Okay, so the gun has a little kickback; so what? Well, let's look at the bullet's kinetic energy, calculated from the equation:

KE = ½mv²

Hence, the kinetic energy of the bullet would be:

The impact of our bullet would be like blowing up over 1000 tons of TNT. Needless to say this would take out a little more than just Vanessa Williams.

Of course, with such deadly power, good aim is still essential. Thankfully, our weapon is equipped with a special x-ray sighting system, which magically allows the assassin to see through walls. In the real world, when a patient is x-rayed at the doctor's office, the rays are absorbed by his bones while passing through the rest of his body. Exposing a photographic plate to the x-rays as they exit the patient's body reveals a silhouette of his skeleton where the x-rays have been absorbed.

In Arnie's world, however, bones (and other miscellanea) reflect the x-rays back to the scope, allowing the assassin to see his victim's skeleton through walls. The only place for our heroes to hide is behind the refrigerator, kryptonite for super assassins with x-ray scopes, as our movie-makers would have us believe.

We haven't even mentioned the ludicrous scene of Arnie hanging out the door of a jet aircraft with one hand as he reaches for a parachute, which is then thrown overboard. He nearly hits the jet's engine when he finally lets go, defying laws of gravity and projectile motion not to mention common sense. And why would he wait seven seconds before following the parachute? We suspect this movie could well become a classic of insultingly stupid movie physics.