Understanding Movie Physics: Eraser

Arnold Schwarzenegger. Action scenes. Rail guns. Inaccurate physics. All of these factors contribute to the thrill that is the movie Eraser. However, it's that last factor, inaccurate physics, that tends to bug many of this movie's viewers. Especially the physics that violate the law of the conservation of momentum.

The scene posted below, like many of the other's seen throughout of the movie, show a human, often either Arnold's character or one of the enemy thugs, firing a weapon called a rail gun. In the movie, a rail gun is explained to be a gun that uses electromagnetic energy to fire a lightweight aluminum bullet at almost the speed of light, and it is here that we discover the inaccuracy of these scenes.

Eraser Scene:

https://youtu.be/IDC-tIQpJ_0 

Whenever one of the speeding rounds hits a human body, that individual is most often sent flying across whatever environment they are in , but the shooter is always left unaffected and in the same position as they were before. This is the violation of the law of  conservation of moment as previously mentioned, which states "In the absence of external forces interacting upon an object or a system of objects, the total momentum will not change". This basically states that the momentum before and after the collision must be the same. Therefore the shooter must face a negative recoil velocity that sends them flying backwards that is equivalent to the positive velocity of the bullet being shot forward in order for the momentum's of each object to cancel each other out and get a total momentum value of zero that was present before the collision. Another approach is that neither the shooter or the one shot face any kind of momentum that would send them flying and instead don't get sent flying like before.

Due to the complete disregard of the law of conservation of momentum, I am rating this movie with an RP (retch physics) rating.