Ahh, the gravity gun. What a wonderful device. Anyone who has played Half-Life 2 for a while, or even watched the videos, will know of this joyous implement of destruction. Rather than just hurling bullets at your foes, hurl the environment: The Ravenholm Level with saws scattered everywhere was worth the price of admission alone, but in latter levels it becomes even more beautiful as you can hurl not just boxes, crates, and explosive barrels around, but your enemies themselves.

But what are the real physics behind this object? It seems to be able to pick things up, and shoot them a high velocities, but Gordon has a PHD in physics, surely there's some hard science to back it up.

Lets go to the equations: F = {m rsub 1 m rsub 2 G} over r^2 : Quite simply, the basic law of gravity. Force between objects resultant from gravity equals the mass of one object time the mass of the other object times the gravitational constant, all over the distance between the objects squared. We also know that F= ma, force equals mass time acceleration, so the final equation is A= {m rsub 1 G} over r^2, Acceleration on one object towards the other equals the other's mass times the gravitational constant over the distance squared.

From some rough tests in game, I set up a standard small wooden crate, which I assume to be about 10 kg (though its weight will be irrelevant according to the above), about 20 meters away from me. I then proceed to attempt to draw it in with the gravity gun. This results in it accelerating towards me at a rate of about 1m/s^2. Combine that with G at 6.67259 * 10-11 N m2 kg-2, and that means that the gravity gun is has created 11,989,347,464,777 kg in the space in front of you. Wow.
Note: the euqations used here are from StormHunter's writup in Acceleration due to gravity, though they match my high school physics knowledge.
Further note: Don't node at 1:30 am after a too long bout of HL2