Bullets

I had quite a horrible mental breakdown over the weekend, a proper mental breakdown and not some blog hyperbole, and as a result I've decided to keep myself a bit more busy over the coming weeks. This should hopefully extend to this blog too.

With all that said, off to yet another post of inane pedantic drivel...

In a somewhat similar vein to my last post, the subject of movie physics, I plan to talk about bullet sparks.

Simply put, they're a load of bullshit. Bullets don't spark like what you see in some films and most TV shows. The reason for this is very simple, they're made out of copper-clad lead or lead alloys and not steel.

It's why some hammers, used in chemical industry or other places where a spark could be very fatal, are made out of lead (or copper alloys) and not steel.

Bullets do get hot when they strike solid objects. The worst case would be if all of a bullet's kinetic energy were instantly converted to thermal energy when a bullet struck its target and all the thermal energy remained inside the bullet. This is highly unlikely but easy to calculate. I say easy...

A .45 cal handgun bullet (it's a big enough bullet, in between (ish) a standard 9mm and Dirty Harry's
.44 mag), has a mass of 0.015 kg and a muzzle velocity of around 288 m/s. Kinetic energy is calculated from the mass and the magnitude of the velocity of an object using the following equation...

KE = ½mv2

KE = kinetic energy m = mass v = velocity

Using the above equation and the values I supplied we find that such a bullet has a kinetic energy of 619 J. And if all that kinetic energy is converted into thermal energy the temperature rise is calculated as 324° Celsius.

If the bullet starts at room temperature (24° C) it will end up at 348° C. The melting point of lead is 328° C.

So, in this highly unlikely event that all the kinetic energy turns to heat, in a hope to generate a spark, the lead would melt. And molten lead looks like silver. In fact molten lead is used in films as a substitute for molten silver.

All worked out on the basis that the shot was at point blank range.

Of course bullets don't get that hot and most of the kinetic energy is lost on it's short travel.

Unlike last weeks post, where I made the point that lasers in films work how they do because otherwise they'd be boring, sparking bullets are just shit.

Subtlety can be far more dramatic­