Physics Has Been 'Erased'

Behold! The railgun! What is a railgun you ask? It is a terrible weapon that uses electromagnetic force to launch its projectile at crazy high velocities. The military and NASA have created versions of their own which are absolutely massive. But in the case of the movie Eraser, they're basically the same size as an average AK. But that's not the only issue in this movie. These railguns in no way abide by the laws of physics, specifically the conservation of momentum.

So usually, when a person fires a gun, there is a bit of a recoil, but that is what the shoulder stock is partly for on some bigger guns. This is due to the law of conservation of momentum. Since both objects are originally at rest, after firing a bullet with positive velocity, there must be a negative velocity to equal it out. If this is the case for the railguns seen in the movie, then something just isn't adding up. The aluminum bullets fired from the gun are said to have a velocity close to the speed of light, which is 299,792,458m/s. With the bullet being very lightweight, Arnold Schwarzenegger being a bit over average mass (114kg) and having a velocity of 0m/s, the velocity inflicted on the bullet should also be applied to the shooter. This would send Arnold flying almost as far as the aluminum bullet, and subsequently, the enemy who gets hit. So as Arnold is standing there, merrily firing away (see above), this movie is getting an RP (retch physics) rating for not conserving momentum. Momentum deserves to be loved too!


  1. Nice writing. Be a little bit more careful in the future distinguishing physics concepts. Velocity and momentum are not the same thing. Momentum is a conserved quantity, velocity is not. As you kind of get into, but don't make quite clear, since Arnold is significantly more massive than the aluminum rounds, his recoil velocity will likewise be significantly less. BUT, the speed of light is so ridiculously large, that even 1/10,000th of the speed of light would be a crazy fast recoil velocity.


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