How does mass and velocity affect the amount of damage?

Question

I’m not a science-y person, but I love sci-fi. In a novel I read near a decade ago (Larry Niven’s Known Space series), he mentions occasionally kinetic weapons. I’ve seen this online as well with tungsten-based projectiles being discussed. So my question is how does mass and velocity affect the amount of damage? If I had a nickel-sized object, how fast would it need to go to cause city-wide devastation (would it be possible or would the damage output be capped based on either size or velocity)? Conversely, If I launched something at the speed of sound, would the damage output be the same if it were different-sized objects?

In: 5

Answer 1

Look no further than the crater made by a meteorite. The rock that impacted is many times smaller than the diameter of the impact crater. But it was moving fast, on average rocks hit planets and moons and one another at around 18km/s. Some have been known to hit at even higher speeds, 30, 40, even maybe 50 km/s given the right conditions.

When you catch a ball, does it just lightly land in your hand, or can you feel it “smack” your hand as you catch it? It had velocity, and it has mass. When you caught the ball, it transfered that potential energy into your hand. What happens if I throw the ball faster? Bigger smack. What happens if I throw a heavier ball?

Let’s say I lob a tennis ball at you, you’ll be able to catch it with one or two hands, no sweat. If I throw a bowling ball along the same trajectory, you will need two hands, and you will probably need to take a step back as you catch it to stop it knocking you over – because you need to send that momentum somewhere.

The more mass something has, the harder it can hit – it takes more force to stop it. The faster something is going, the more energy was used to get it going that fast, the more energy it will take to stop it. So naturally something with more mass and more velocity will just hit harder.

Tungsten has a pretty high density – its fairly massive (heavy) and conversely pretty rigid. Get a 0.5m chunk of it moving, say with a rail gun in a vacuum at 100km/s, and there you have it, a kinetic weapon.