Kinetic Question

Kitsune · Post by **Kitsune** » 2006-05-24 06:09pm

I have been discussion battleship guns on spacebattles. Turn of the Twentieth Century U.S. Naval Guns fired a much heavier shells than German Guns as seen by this table

His comment is:

And, as I've already pointed out to you in a previous thread, these stats look nice, however, they are pretty meaningless unless you intend to fight an action where both sides are a few hundred yards apart, for accurate figures can be determined using the actual impact velocity, as opposed to muzzle velocity, and then factoring in things like quality of the shell, dynamics of the shell, angle of fall, etc. These make up actual penetration tables.

I responded:

What you are attempting to do is dismiss American Shells. Is it or Is it not the case that in basic physics that a heavier shell will carry more of its kinetic energy at a longer range than a light shell. Yes or No? I want a real answer since you suppose to be an engineer! Second, did or did not D.K. Brown state that U.S. shells were generally superior to U.K. Shells?

Does anything to help me with my statement or mistakes I might have made?

Covenant · Post by **Covenant** » 2006-05-24 06:21pm

You seem to have it right. They seem to all be moving at the same relative speed according to your chart, which means that the heavier shell was given a lot more acceleration. So the range should be greater for the big shell, given that it has a higher amount of inertia to allow it to push through air.

Plus, big shells can go up real high and crash straight down and use all that mass to drop on the deck nice and hard, smashing through away from the belt armor. And heavy shells go through water better, allowing them to undershoot the belt and hit low on the ship.

From what he's said he seems to be reminding you of basic shell principles without looking at the numbers. Impact velocity will be greater for a big shell than a small shell, given that they both have equal muzzle velocity, because heavy things will slow down slower. He should agree with you... I have no idea why he isn't. He could claim UK or German shells were made better and US shells would fall apart on impact, but that's just silly, and not true. Now, our torps on the other hand...

Pezzoni · Post by **Pezzoni** » 2006-05-24 07:26pm

I guess he is partially correct: depending on the shape and areodynamics of the shells etc, they will differ in the percentage of the energy at muzzle that actually reaches the target. I can't seriously imagine this making a difference of 50-70MJ however.

lPeregrine · Post by **lPeregrine** » 2006-05-24 08:05pm

In Ideal Physics Land (with no friction, drag, etc), if velocity is the same, the heavier shell will be superior. But in the real world, things like the shape/size of the shell, flat vs. high arc, etc all are extremely relevant. What he's saying is true, you can't just look at muzzle energy to answer questions about penetration at long range.

Keep in mind that kinetic energy = 1/2 mass * velocity^2. So changes in velocity (like you'd get from drag/high arcs/etc) can actually have a much bigger effect than the same factor multiplied on the object's mass.

Of course I don't know anything about warship gun penetration, so you could easily be right. All I'm saying is it's not quite as simple as just comparing muzzle energy, unless the penetration is at point-blank range.

Kitsune · Post by **Kitsune** » 2006-05-24 08:24pm

Friction is effected by surface area and surface area increase by the square of the size while volume (and mass) increase by the cube of the size of the shell.

Kitsune · Post by **Kitsune** » 2006-05-24 08:34pm

Also, if it was within around 10%, I would agree with you but we are talking about at least around 25% and sometimes as high as 65% more energy.

Post by **Darth Wong** » 2006-05-24 08:51pm

Aerodynamic drag forces are a function of frontal area and coefficient of drag, which in turn is a function of shape and surface texture. I find it highly unlikely that there would be a dramatic change in the frontal area, shape, or surface texture of shells. The frontal area is a simple matter of cross-sectional area calculations unless it's turning cartwheels in the air, and it's not as if we're talking about complex shapes here where there were a lot of changes and experiments, so I would say the onus is on him to back up his claim that there were dramatic differences in the shape of American and German shells.

Kitsune · Post by **Kitsune** » 2006-05-24 08:59pm

Darth Wong wrote:Aerodynamic drag forces are a function of frontal area and coefficient of drag, which in turn is a function of shape and surface texture. I find it highly unlikely that there would be a dramatic change in the frontal area, shape, or surface texture of shells. The frontal area is a simple matter of cross-sectional area calculations unless it's turning cartwheels in the air, and it's not as if we're talking about complex shapes here where there were a lot of changes and experiments, so I would say the onus is on him to back up his claim that there were dramatic differences in the shape of American and German shells.

He made no such claim in multiple discussions......curious is that enough to show that he is likely not the Engineer he claims?