I'm sure everyone reading this knows what a sniper rifle is. You know: long barrel, cylindrical scope, big long bullets, used for long range and heavily armored targets. But, what you might not know is how powerful one is. The standard NATO sniper rifle bullet is the .5 BMG. Made in 1921, the most powerful version of that cartridge is about .052 kg, and leaves the rifle at 882 m/s. p = mv, so p = (.052)(882) = 45.86 Ns. That big fat hunk of copper has about 50 Ns of life in it. Now, the average adult human head weighs about 4.5 - 5 kg. Seen as how I'm writing this I'll use myself as the test subject. I'm not quite an adult yet, so let's say 4.5 kg. One day, a friendly physics teacher near you sees just way too many tests in one day, pulls a standard issue sniper rifle out of his attack and takes a pot shot at some weird kid. Naturally my head pops of like a tootsie pop in that owl cartoon. Assuming the bullet finds a warm new home in my cranium, that's 10.08 m/s it pulls my dome along with. The average height of a 17 year old male teenager is about 1.75 m. Assuming that the bullet is fired horizontally, we can use kinematics magic to find that my head hits the ground 6.02 m away from my toothpick body, and rolls whocares m afterwards. Doesn't sound fun does it?
That's why I'm proud to present to you our newest innovation in protective headgear: the tank hat. This simple helmet is made of solid 6" steel and can protect you from bullets, mortar, bullies, and apples. Teach Newton a thing or two today!
--Warning, tank hat does not protect against .5 BMG Armor Piercing rounds. Don't be rude to IHS Physics teachers for your own good--