Can someone explain to me the science behind an asteroid collision?

Pour a small pile of table salt into your hand. Now blow on it.

What happened to the salt?

It is true that the Russian meteor did not actually hit the ground. The meteor exploded during reentry because of the the intense heating and air pressure caused by reentry. This explosion occurred roughly 18 miles in the air, and was 20–30 times more powerful than the atomic bomb dropped on Hiroshima. It was the shockwave from this explosion which caused all of the damage.

This isn’t the first time this has happened. In 1908, an even larger event occurred over Siberia. That explosion, also in midair, was 1000X more powerful than Hiroshima.

For a really destructive “modern” asteroid, check out the Tunguska event. The Wikipedia article has a lot of text, and you can search for images, too that will give you a very graphic view of what “a small asteroid or comet” can do to Earth.

The destructive power of an asteroid is easily appreciated if you just visualize a large mass (say the size of your house) traveling at several times the velocity of a bullet. Remember that both the earth and the asteroid are already hurtling through space at velocities measured in miles per second! If the paths of the 2 objects intersect, the earth’s attraction would INCREASE the speed at which the asteroid would approach our planet. It isn’t true that you couldn’t see it coming. If you knew where to look, and had the proper telescope, you could probably watch the approach for days depending on the size of the asteroid. If you were watching with your naked eyes when the thing hit the earth’s uper atmosphere, you would be permanently blinded as your optic nerve was fried by the intensity of the light, but the thing would be traveling at a speed so great that it would have struck the earth before you were aware that you’d been blinded.

Random chance.
If you were directly in front of one that was going to hit the Earth, and not explode in air, it would kill you instantly with the shock wave that it’s incredible speed creates just ahead of it. But you would be smashed to smithereenies is the following instant so what exactly killed you would be moot. If you are off to the side the shock wave it leaves in it’s wake (like the wake a boat leaves in the water) will kill you by concussion, like a bomb or heavy artillery shell blast.

Purdue University has an online simulator/calculator called Impact Earth! that you can use to experiment with various asteroids and see their predicted effects. You can change size, material, velocity, target, etc. and it will tell you energy, global damage, crater, seismic effects, air blast, thermal damage, etc. You’ll love it.
Chicken Little was right!

Consider catching a baseball tossed underhand and one thrown overhand. The difference of the impact upon your gloved hand is a function of its speed. The power of an asteroid is the product of its mass and velocity.

What fascinates me though is how grand the shockwave can be hundreds of miles away. I saw some documentary on them and they said that a formidable asteroid would decimate Washington DC even if it hit NYC. But now that I’m realizing just how fast they are going, it’s no wonder.

@stanleybmanly I see. So now that I think about it, the movie “Seeking a Friend for the End of the World” really has the best depiction of what an asteroid impact would feel like? I probably just ruined it for anyone who hasn’t seen it but it’s not like it’s a huge spoiler. But basically at the end it’s kind of like that – a boom and a flash of light and cut to black.