Gravity/Physics Question

fedorable1 said:

Newton's First (or maybe 2nd) Law states that every action has an equal and opposite reaction. So, if someone shot a gun in outer space, would they be shot backward at the speed of the bullet?

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I think you are thinking of Newton's Third law. When a gun shoots, the gun itself is propelled backwards (recoils) with force equal to that propelling the pullet. If someone is holding on to the gun, they will be pushed backwards as well. However, the gunner would not be shot backward at the speed of the bullet, because a person has a much larger mass.

The force initiating the movement of the bullet will be equal in force to the body but proportional to weight and mass. Even in no gravity situations the body is more of an opposing force than the bullet.

space is a vacuum - no molecules floating around in the air. How does that affect the bullet and the recoil?

Tish Davidson said:

no molecules floating around in the air.

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Not just no molecules floating around in the air--no air, even.

How would it affect the bullet? Well, it would keep going until acted on by another force.

I don't think it would affect the recoil.

Bullet

The cartridge, of course, would have to have been put together on earth, would have to be airtight, and would have to have enough oxygen sealed inside the brass to allow the gunpowder to burn. No oxygen sealed inside the brass, no burning gunpowder, no shot fired, no recoil at all.

Having said this, recoil is a good deal lighter in outer space. One of the things that makes recoil so severe is the air inside the barrel of the pistol. A bullet accelerates instantly to several hundred feet per second, and the air inside the barrel must be pushed out of the way. The air compresses, fights against the bullet, and this increases recoil greatly.

i dont think so, how ever the shooter, if also in space will feel the recoil.
the shooted , depending on the penetration power of the bullet will either
a. go through the target
b. knock the target back slightly, (the bullet had maybe a 1000th the mass of a human

the most that might happen is that the target will be throw into a head spin, again, depending on were the bullet struck

Jamesaritchie said:

The cartridge, of course, would have to have been put together on earth, would have to be airtight, and would have to have enough oxygen sealed inside the brass to allow the gunpowder to burn. No oxygen sealed inside the brass, no burning gunpowder, no shot fired, no recoil at all.

Having said this, recoil is a good deal lighter in outer space. One of the things that makes recoil so severe is the air inside the barrel of the pistol. A bullet accelerates instantly to several hundred feet per second, and the air inside the barrel must be pushed out of the way. The air compresses, fights against the bullet, and this increases recoil greatly.

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Unfortunately, this is all wrong. Oxygen is not needed as the powder contains its own oxidizer. And no, the air in the barrel has little to do with recoil. It does decrease the speed of the bullet slightly, so that reduces the recoil slightly, but not enough to matter.

When it comes of guns and recoil in space, just remember that mass is the important thing, not weight. On the moon, you weigh one sixth of what you weigh on earth. In space you are weightless. In both cases, however, your mass is the same as on earth. And it is the mass that is important here, not weight.

Working out the force of recoil is the least complicated of all in space, because the vacuum means that there is no friction.

Julie Worth said:

Unfortunately, this is all wrong. Oxygen is not needed as the powder contains its own oxidizer. And no, the air in the barrel has little to do with recoil. It does decrease the speed of the bullet slightly, so that reduces the recoil slightly, but not enough to matter.

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Well, yes and no. I didn't mean to say the gunpowerder wouldn't burn at all. It does. But having its own oxidizer does not means it burns as fast, or builds up enough external gasses to propel a bullet at several hundred feet per second. The air inside a cartridge makes a big difference. Try firing one in a vacumm, with a vacuum packed cartridge, and see what happens. There's also a noticable difference in recoil when a weapon is fired in a vacuum.

Recoil is significantly less when fired in a vacuum, and it is because of the air in the barrel. It's not only the friction, it's the conpressed air wave caused by the friction. The air inside the barrel makes the bullet itself act as if it had more mass. I've fired pistols in vacumms, and the difference in recoil is quite noticeable. If there's another cause of the difference in recoil, no one I know can determine what it is.

This does depend on bullet type. A pointed bullet is much less affected, a round bullet with a big hollowpoint is affected to a much greater extent.

It's not nearly as bad as the silly scene in Firefly where they pumped oxygen into a gun barrel in order to make it fire at all, but both factors do make a very real difference.

Of course, when you fire a weapon in space, you won't be propelled straight back at all. What will happen is that most of the energy will be utilized in spinning you about your axis. There is backward motion, but how much is very difficult to determine because it all depends on where and how you hold the weapon.

Recoil is also affected by how tightly the bullet is being squeezed by the brass casing, which also makes teh bullet act as if it had more or less mass, by bullet diameter in relation to land and groove diameter, and even by the number of grooves.

There are two "kinds" of recoil, real and apparent. Real is a straight scientific value of mass and energy. Apparent is all these other factors, and they do affect recoil significantly. "Real" doesn't happen unless you remove all other factors. "Apparent" is what a shooter actually deals with.

Go to www.space.com and find the message board there. Ask your question on the Ask the Techi a Question thread.



I have asked questions there concerning the break up of a moon, and how long would it take to form a ring around a planet. I got a lot of information concerning the gravity well and the decline that all rings eventually go through.



If you consider the ion drive engine you will see how a nominal propulsion system can theoretically... uh... propulse?... an object through space.



One thing aside, space is a vacuum, but it is most definitely not empty. There are countless billions of particulates in varying areas. Just not enough to cause any positive pressure.

The above is simply IMO, and bears no official scientific proof.