In a climactic scene in the new sci-fi actioner Total Recall, our heroes Hauser (Colin Farrell) and Melina (Jessica Biel) find themselves caught in a zero-gravity shootout near the center of the Earth. Would guns really work in zero gravity?
Yes. Unlike most ballpoint pens, for example, which are famously ill-equipped for the weightlessness of outer space, gravity has nothing to do with the mechanical functioning of a gun. Instead, both semi-automatic and automatic guns rely on springs (not gravity) to bring the next bullet into the chamber, before a small explosion within the gun fires the bullet.
However, as in the film, a zero-g gunman should exercise some caution, as firing a bullet would also send him or her flying in the opposite direction. When you shoot a gun under normal conditions on Earth, the friction between your body and the ground keeps you in place. With every shot you experience recoil (your arms and shoulders are forced back by the force of the bullet’s projection), but with an experienced shooter it’s only about an inch to a foot, and you should have no problem staying on your feet. In zero gravity, on the other hand, even the smallest recoil would send you backwards. In most cases this would be very manageable, however, bouncing you back at a speed of less than one meter per second, so you wouldn’t have to worry about seriously injuring yourself. Even if you fired a .44 Magnum, for example, and weighed only 100 pounds, the recoil velocity would be under 0.5 mph, which is still less than walking speed. If you wanted to really propel yourself using a gun, you’d want to use a really big one.
What about the bullet? Would it be more quick and deadly in space? Not really. The speed of the bullet would remain roughly the same in zero gravity as it is on Earth, so shooting in space is not going to make your gun any more or less lethal to your space enemy. The only way you’d see a noticeable difference is if you were firing the bullet over a long distance. On Earth, a combination of air resistance and gravity slows the bullet and gradually pulls it down towards the Earth. This is why when you shoot your weapon, you have to aim slightly higher than your target. This force is so small, however, that over short distances there would essentially be no difference in the shot’s trajectory.
Thanks to Dr. L. Nelson of Bishop’s University and L.P. Brezny of Metro Gun Systems
smo wrote:Isn't there an issue with oxygen for the burn to take place as well? (Assuming you aren't in a ship of some short that is oxygenated...)
smo wrote:Good point. I've never played much with gun powder, so I don't know if it contains everything needed for combustion or not.
Hawk87 wrote:The force of gravity changes by the square of the distance from the center of the mass. Doubling the distance reduces the force by a factor of 4, and vice versa. There for the force of gravity should be quite a bit greater near the center of the earth. I don't know about the EXACT center, but it would be a very small point of space.
bagpiper wrote:Hawk87 wrote:The force of gravity changes by the square of the distance from the center of the mass. Doubling the distance reduces the force by a factor of 4, and vice versa. There for the force of gravity should be quite a bit greater near the center of the earth. I don't know about the EXACT center, but it would be a very small point of space.
It actually depends on what is at the center of the earth. If the center of the earth is a void, then there is no mass there to attract. As the void gets larger, there is more and more area where the gravitational forces will be either zero, or very low. Of course, as the void gets larger, there is also more distance to accelerate as you are drawn toward the mass on the outside edges. Imagine the "earth" as a giant basketball: all the mass concentrated in a very thin shell and huge empty void in the center. At exactly the center of that void there is zero net gravitational forces. But move away from the center and now the gravitational pull is stronger form one side than the other and you will be drawn toward that edge. The closer you are drawn, the stronger the net force pulling you will be and you've got a nice 4,000 mile radius from center to edge to accelerate. Unlike being in orbit above the earth where you can move forward at a sufficient rate that you constantly "fall" around the earth, when you are inside, rather than outside the sphere, there is no way to miss the earth.
I recall vaguely a science fiction book years ago based on the premise that the earth was hollow and there a civilization (or two) that lived on the inner edge of the earth's crust. At that point, gravity on the nearby edge a fair bit stronger than the pull from the other side that is some 8,000 miles distant, overhead.
Car Knocker wrote:smo wrote:Good point. I've never played much with gun powder, so I don't know if it contains everything needed for combustion or not.
Gunpowder contains an oxidizer, so doesn't need atmospheric oxygen to burn. Think about it: a cartridge in a semi-auto ignites, the case seals against the chamber wall and the bullet seals the rifling...where does the oxygen come from for the combustion process?
sarahbn wrote:Srry if I made a breach of etiquette, I was running out of break time.
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