Sunday, September 13, 2015

Eraser and the Physics Defying Railgun!

This week we at the Physics in Film class, we watch Eraser from 1996 with star, Arnold Schwarzenegger. We will be using the scene the railgun is first used in the movie. It was where the gun was used to kill Lee Cullen's ex stalker boyfriend (Mr. break into the house and take a shower while I wait).  When the ex-boyfriend was shot, he was heading to get down *insert Arnold saying "GET DOWN" here* and when he was hit, he flew back and was pinned against the wall. Railguns known for their penetration power and in this movie "known to shoot bullets at the speed of light" wouldn't have pinned the guy against the wall. At the same time, we have to see how the sniper was able to shoot the gun with barley any recoil to it at all. *Seems like bologna to me*

For this I analyze what was need for this.
I looked for the average of humans (80.7kg), of assault rifles (3.99 kg), and of an average bullet (0.00454kg). I looked and estimated some of what was need for the velocity of each object, most almost not having much or any at all. If the shooter shot the railgun with no or minimal recoil, means that it didn't move him or changed his velocity which consisted of 0 m/s. If the bullet went at the speed of light then it's velocity would have been 299,792,458 m/s. The boyfriend stalker was falling to the ground so I estimated his speed at .46/m which is close to 3 mph. Using these I would find the momentum of the bullet and see where the energy carries on for both the shooter and for the stalker boyfriend.

After seeing the work, you should be able to tell the the energy from the railgun being shot, should have given a strong amount of recoil, that should have either sent the gun flying and maybe even the shooter too.

As for the boyfriend, he shouldn't have been pinned to the wall as he was. The bullet would have broken through the body and kept going. It is quite possible that it could have vaporized the body, leaving a giant hole, or maybe even nothing at all. The body would have also gone farther in distance compared to the distance he flew from where he was to a wall that was about maybe 3 meters away.

Seeing the analysis, the movie defies Physics and isn't accurate to an actual railgun that in this current day can only shoot bullets at the speed of 2500 m/s. The only real railgun that we've seen was the one from the Navy, which shoots aluminum rounds that are the size of about 70 mm rounds (guess/estimate). 

1 comment:

  1. OK, it looks like you calculated the "missing" momentum in the first part of the problem, although I am not sure why the shooter and gun had any initial momentum. A lot of your variables are lacking units, too, which can be a problem. You also took Daryl's final velocity to be zero, but that's only after yet another collision - Daryl's collision with the wall. We want the velocity of Daryl immediately after he is hit by the bullet.