Gun

Hollywood and Physics

We’ve all seen these kinds of movies. After a fast and dramatic chase, the bad guy jumps out of the car, determined to end the good guy once and for all. His evil plans have been thwarted for the last time! In self-defense, the good guy is forced to take a shot and when the bullet hits, the evildoer is thrown violently backwards as a result of the impact and through the nearest shop window. Once the hero is reunited with the love of his life, the credits roll and we are left to wonder if that’s really how physics work.

In a previous example we calculated the momentum of a common 9 mm bullet (p = 5.4 kg m/s). Suppose the m = 75 kg evildoer gets hit by just this bullet. Since the bullet practically comes to a halt on impact, this momentum has to be transferred to the unlucky antihero for the conservation of momentum to hold true. Accordingly, this is the speed at which the bad guy is thrown back:

5.4 kg m/s = 75 kg · v’

v’ ≈ 0.07 m/s ≈ 0.26 km/h ≈ 0.16 mph

This is not even enough to topple a person, let alone make him fly dramatically through the air. From a kinematic point of view, the impact is not noticeable. The same is true for more massive and faster bullets as well as for a series of impacts. The only thing that can make a person fall instantly after getting shot is a sudden drop in blood pressure and the resulting loss of consciousness. But in this case, the evildoer would simply drop where he stands instead of being thrown backwards.

This is not the only example of Hollywood bending the laws of physics. You’ve probably heard the weak “fut” sound a Hollywood gun makes when equipped with a silencer. This way the hero can take out an entire army of bad guys without anyone noticing. But that’s not how pistol silencers work. At best, they can reduce the the sound level to about 120 dB, which is equivalent to what you hear standing near a pneumatic hammer or right in front of the speakers at a rock concert. So unless the hero is up against an army of hearing impaired seniors (which wouldn’t make him that much of a hero), his coming will be noticed.

This was an excerpt from my Kindle book: Physics! In Quantities and Examples

For more interesting physics, check out my Best of Physics selection.

Guns per Capita and Homicides – Is There a Correlation?

Here’s a statistics quicky. A while ago, just after the tragic shooting at Sandy Hook Elementary School, I wanted to produce a clear proof that gun ownership and homicide rates are correlated. It seemed logical to me that, plus / minus statistical fluctuations, the phrase “more guns, more violence” holds true. So I extracted the relevant data for all first world countries from Wikipedia and did the plot. Here’s the picture I got:

Graph2

Maybe you are as surprised as I was. Obviously, there’s no relationship between the two variables, more guns does not mean more violence and less guns does not mean less violence. So whatever the main cause for the violence problem in the US (see the isolated dot in the top right? That’s the US), it can’t be guns. And that’s a liberal European speaking …

Just in case anyone cares, I blame the gang and hip-hop culture. I can’t be guns (see above), but it also can’t be media or mental health or drugs (people in all other first world countries also play shooter games,  watch violent movies, have mental problems, buy and sell drugs).

Sources:

http://en.wikipedia.org/wiki/Number_of_guns_per_capita_by_country

http://en.wikipedia.org/wiki/List_of_countries_by_intentional_homicide_rate