Ricochet on walls

[Winston]

Why do bullets tend to stay paralell when ricocheting against walls?

I thought the angle of incidence equals the angle of reflection?


Thanks

[Preacherman]

That's for light.

Bullets aren't light.

They're heavy.

:neener:

(Sorry - couldn't resist that! :D )

[RyanM]

Short answer is they don't. Bullets can go in pretty much any direction after hitting any object. Why do they do that? Other short answer is because they deform. If you were shooting diamond ball bearings at diamond walls, they'd behave more like you'd expect a perfectly elastic collision to.

[svtruth]

a superball down a cinderblock hallway. Each wall/ball collision imparts reverse spin to the ball and it eventually bounces pretty much straight back and forth.
Yeah, I didn't tak grad school too seriously.

[John Hicks]

The walls deform too. Don't think of it as a round object striking a flat surface.

The bullet hits the wall and both deform. If the wall is soft enough, it will actually crater a bit and as the deformed projectile "leaves" the crater, it hooks on the lip a bit. This changes the trajectory and spin of the projectile, as well as takes energy away from it.

Angle of imact is very important. If you shot down a hallway and hit the wall at a 45 degree angle, the bullet would deflect out shallower than 45 degrees coming off the wall. If you shot closer to 90 degrees perpendicular to the wall, the round (if it ricochet'd) would come more or less straight back, as you'd expect.

But then there's a critical angle when you are firing down a hall. It's shallower than 45 degrees (i.e. shooting more down the hallway than at the walls), and when the bullet hits the wall, the spin imparted to it on the bounce acutallly forces the round towards the same wall again (similar to a curve ball). The result is a bullet skipping down a wall until it loses enough speed or altitude to be harmless. It's a neat phenomenon and it's also why patrols on streets don't hug the walls while moving (if they don't have to for cover). The particular angle is determined by bullet composition, velocity, and wall composition, so it could vary quite a bit.

Unfortunately, I forget where I read the technical details of how this works. However the phenomenon of "skipping" is discussed in the book "Black Hawk Down".

JH

[rwc]

Isn't the same true for halls and corridors? I.e. - stick to the middle and don't hug the walls?

[JohnKSa]

I thought the angle of incidence equals the angle of reflection?That's for inelastic collisions and reflections of rays.

No deformation, no friction. They teach that stuff in school because there are simple answers and formulas. ;)

[BigBink]

Read somewhere .......can't recall the source, that the common TV ploy of hugging a wall in a long hallway is a bad idea. The article claimed that bullets hitting a wall with just a glancing blow tend come off at a specific angle of 12 degrees. Therefore they stick pretty close to the wall so you might be safer in the center of the hall. I know, your physics 101 prof might not agree but then he is probably an Anti anyway.