Does a bullet fired with a clockwise spin travel faster or slower

[Phrak]

Obviously there is some debate between energy and stopping power possessed by a bullet. Now I am no expert on firearms or ammunition, but here is my take:

A smaller bullet my be able to be fired with a greater velocity thus increasing its kinetic energy greatly since KE=(1/2)mv^2. But if a small bullet encounters less resistance while traveling through the target then it will leave the target with some velocity left. So the energy transferred to the target is equal to the difference in kinetic energy of bullet (neglecting heat, etc.).

Now a larger bullet may carry less initial kinetic energy, but experience enough resistance to stop somewhere in the target (or at least come out with a much lower velocity). Because of this the change in KE and thus energy transferred will be greater.

Of course this is not taking into effect the tumbling of the bullet within the target. If a small fast bullet tumbles withing the target then its velocity will greatly slowed or stopped causing much greater stopping power. I've heard of those little 22 caliber bullets people like to make fun of doing a lot of damage because of this. They enter the target tumble around and don't exit. So in a pure physical sense stopping power is only related to the amount of energy transfer. Taking into account what vitals are hit and bleed out times is an entire different story. This is only talking about the stopping force felt.

Hollow point bullets are designed to mushroom and/or fragment on impact--therefore more 'stopping power'.
Mushroomed 9mm.

 

[Tyrannical]

I fully understand that, but that doesn't mean it reduces air resistance.

The air resistance a spinning bullet undergoes is equal to that of a non-spinning bullet. It's not until the bullet is tumbling that this changes. So the gyroscopic forces prevent the tumbling occurring.

However, the air resistance each encounters up to that point is identical. It's only that one reacts and the other is able to resist.

I'm not seeing it as reducing air resistance, more that it has an increased ability to withstand it.

The spinning stabilizes the bullet, because it is stabilized (not shaking, vibrating, tumbling, zig-zagging, etc.) it cuts a path through the air that offers it less air resistance.

 

[JaredJames]

Obviously there is some debate between energy and stopping power possessed by a bullet. Now I am no expert on firearms or ammunition

A larger bullet has more stopping power. There's no debate on that.

A .45 can stop a person more effectively than a 9mm. And a .50 more effectively than that.

Remember, stopping power is not the same as ability to kill or damage done.

 

[Tyrannical]

A larger bullet has more stopping power. There's no debate on that.

A .45 can stop a person more effectively than a 9mm. And a .50 more effectively than that.

Remember, stopping power is not the same as ability to kill or damage done.

No, stopping power is determined by how much energy is transferred from the projectile to the target. It is affected by both the mass and velocity of the bullet, as well as to how it behaves when it strikes the target.

 

[JaredJames]

No, stopping power is determined by how much energy is transferred from the projectile to the target. It is affected by both the mass and velocity of the bullet, as well as to how it behaves when it strikes the target.

There is no consensus regarding energy transfer being responsible for stopping power. Please read the articles on stopping power, starting with wiki:

http://en.wikipedia.org/wiki/Stopping_power

Stopping power is a colloquial term used to describe the ability of a firearm or other weapon to cause a penetrating ballistic injury to a target, human or animal, sufficient to incapacitate the target where it stands.

This is the important point here. It is the ability of the bullet to "stop" the target.

If you read on, they mention energy transfer and a few other effects but make it clear that not everyone agrees on which is important and apply to stopping power. Energy transfer is only one hypothesis of stopping power and not well agreed upon.

For a start, momentum plays a far larger part than energy transfer when it comes to stopping something.

A 1kg bullet traveling at 100m/s has a KE of 0.5*1*100² = 5000J
A 10kg bullet traveling at 50m/s has a KE of 0.5*10*50² = 2500J

A 1kg bullet traveling at 100m/s has a momentum of 1*100 = 100kg*m/s
A 10kg bullet traveling at 50m/s has a momentum of 10*50 = 5000kg*m/s

Assuming it hits you square in the chest, the smaller object imparts twice the energy of the larger, but the momentum conservation is far more in favour of the large object. Think of the above example like tennis ball and bowling ball. A 100mph tennis ball to the leg will bounce off (hurt like hell but bounce off none the less). A 20mph bowling ball to the leg will knock you off your feet and also has the potential to break it.

 

[sophiecentaur]

Aren't you describing Shells, rather than Bullets" Plenty of personal firearms have a mass less than 10kg!
For a gun held by a person, the momentum available for the projectile is limited by the amount that will knock him over backwards- in fact a lot less. This can hardly significantly "stop" anyone's forward motion by momentum transfer.
Of course, I know that a good bigun beats a good littleun but as to the Physics involved? That's another question. I suspect it may be something to do with the effect of a hefty shockwave on the nerves of the target, rather than a but of mechanics. Once your knees have buckled, you are, effectively Stopped.

 

[JaredJames]

Aren't you describing Shells, rather than Bullets" Plenty of personal firearms have a mass less than 10kg!

It was an example with deliberately skewed numbers to demonstrate a point. I would have thought that would have been perfectly clear. Or are people here under the impression I believe the average bullet mass is from 1 to 10kg? I take offense to that.

For a gun held by a person, the momentum available for the projectile is limited by the amount that will knock him over backwards- in fact a lot less. This can hardly significantly "stop" anyone's forward motion by momentum transfer.

Please read the article I linked to on stopping power. You aren't necessarily stopping a person dead (bullet hits, they literally stop - I have never said this). Stopping power is only incapacitating them. A 9mm to the shoulder and you may be able to continue coming at me with a knife, whereas a .45 is likely to drop you. Whether people here like it or not, a bigger bullet has more stopping power, despite moving slower and having a lower KE. Moving slower means it has lower KE - so even if 100% of this is transferred to the target, the smaller bullet still imparts more - but the larger bullet still has more stopping power.

Of course, I know that a good bigun beats a good littleun but as to the Physics involved? That's another question. I suspect it may be something to do with the effect of a hefty shockwave on the nerves of the target, rather than a but of mechanics.

Shockwaves on the nerves are only another hypothesis as per the article.

Once your knees have buckled, you are, effectively Stopped.

Precisely. And that's what stopping power is. The tennis ball may do a fair bit of damage so far as hitting me and causing severe bruising, but it doesn't necessarily stop me immediately.

The only key factor I'm seeing is the bullets momentum, and more importantly its ability to transfer that to the target causing damage. A small bullet is far more likely to pass through you.

 

[sophiecentaur]

Yes.
We're into one of those topics that are really outside the realms of Physics. Unfortunately, people seem to want to quantify things that are unquantifiable in simple engineering terms.
A proper Physicist should take a step backwards here, I think. Fools rush in. . .

Btw, if a tennis ball hit me hard, I'd stop and go home. Am I just weedy?

 

[JaredJames]

Yes.
We're into one of those topics that are really outside the realms of Physics. Unfortunately, people seem to want to quantify things that are unquantifiable in simple engineering terms.
A proper Physicist should take a step backwards here, I think. Fools rush in. . .

I don't see why it's outside of physics.

Simple, certainly not. It's an exceptionally complex subject.

I'm not trying to explain it, but simply point out how people can't make blanket statements and try to explain it with only "it's the energy transfer".

My post is only to demonstrate the importance of momentum when looking at the issue and not writing it off to only energy.

 

[JaredJames]

Btw, if a tennis ball hit me hard, I'd stop and go home. Am I just weedy?

If a tennis ball hit me at 100mph, I'd probably keel over. But I'd be damn glad that it wasn't a bowling ball.

 

[sophiecentaur]

I say it's outside Physics because all the interesting considerations (once you have calculated the Momentum and K.E. - School book work, actually) are Physiological and specific to anatomy or even Psychology.

I can't really attach as much importance to Momentum as I do to Energy where a bullet hits a human body because I would think that the actual damage done relates more to Energy. There are grisly details like the shape / area of the bullet as it goes through the body which would affect how 'usefully' the bullet's energy is transferred (matching the energy source to the load, if you like). But there may well be momentum transfer issues where impact with bones is involved.
That reminds me - we're having steak for dinner.

 

[DarioC]

How about a 45 vs a 357 magnum? Got the flu here, really bored. Chuckle.
DC

 

[sophiecentaur]

Get well soon. Plenty of sleep and liquids.