physics of a falling bullet

[para.2]

Last New Year's Day (2002) I came out in the morning to find a brand-new hole in my windshield, and an ( apparently)7.62 AK bullet on my dash board. Bullet didn't have enough velocity to penetrate the dash after going through the glass, but if that had been somebodies head?....

 

[Drue]

On New Years Day, 1992 I found a hole in my windshield and a 230 FMJ .45 slug on the floorboard of my car. The bullet may have deflected somewhat passing through the windshield but a stringline between the hole and the dent on the floorboard indicated that it was going almost straight down.
I still have the slug.

Drue

 

[Mike Irwin]

Fast,

My comment addressed this statement in your first post...

"Every year there is speculation about people shooting into the air..."

The word UP leaves a lot of room for interpretation.

Technically, 1 degree above horizontal is up.

I sincerely doubt that anyone who is stupid enough to fire randomly into the air is really concerned about getting the muzzle of the gun elevated to the point where the returning bullet isn't going to do any damage.

Hence my comment regarding angle.

 

[Frohickey]

As far as objects of different densities falling at different rates, its not density related, but air resistance related.

A theoretical 'point mass' of infinite density will fall at the same rate as a theoretical 'line mass' of zero density.

A 'heavier' object would fall at a faster rate than a lighter object, but this would be imperceptible. Gravitational attraction is related to the masses of both objects. Earth is very massive. Falling object is not.

As far as terminal velocity of a bullet fired into the air, it all depends on air density, the type of bullet, the angle its fired at, and the muzzle velocity. Its really about how much elevation the bullet was given, the amount of air resistance the bullet encounters, and 32 ft/sec^2 that gravity gave it. But that only counts the vertical velocity. There is also the horizontal component too.

The cops I knew that worked on New Years Eve usually find an excuse to either be indoors during the 15 minutes before and after the stroke of midnight, or they just happen to be under a freeway overpass.

 

[Mike Irwin]

"A 'heavier' object would fall at a faster rate than a lighter object, but this would be imperceptible. Gravitational
attraction is related to the masses of both objects."

Fro,

I'm still looking for the article, but check my note above about denser objects seeming to have some sort of repulsion effect.

Blew my mind when I first read it.

 

[GinSlinger]

Mike--I too have seen that article ("In Search of the fith force" or some-such). Article also related that certain articles tested had different "repulsive" forces. That article was about how, even as physics was coming closer to a unifying theory, there was evidence of a fifth--or anti-gravity--force. The article also related evidence of objects in free-fall being repulsed by a granite cliff.

As to the question of a bullet falling.... In a vacuum a bullet will return to earth at the same velocity as it went up. The gravitational force that slows an object going up (-9.8m/s^2) is the opposite (and equal) of it coming back down (9.8m/s^2) (both |9.8m/s^2|). Adding air resistancee back into the equation makes the math veeery complicated. What we do see though is that a smaller projectile (less surface area) will return at a rate closer to its initial velocity. Therefore, a .22 projectile comes closer to muzzle velocity than a .30 projectile.

GinSlinger

 

[Mal H]

Mike - I believe the article was "Searching for the Secrets of Gravity". The part you're talking about is some experiments performed by Ephraim Fischbach. It was reported in National Geographic, May, 1989.

It doesn't apply to falling bullets, at least not measurably.

 

[faustulus]

Mike,
I see your point about angle, and maybe that is my point. I think that many of these incidents that are reported every year are hits that occur not becuase someone was shooting at a 45 degree or less angle. Hence the bullet still retains much of its horizonal velocity while losing its vertical velocity.

Thanks for the articles, those were interesting. I will have to look up that national geographic article sounds like a must read.

 

[4thHorseman]

You guys have wwwaaayyy to much time on you hands. I sat here and read every post, so I guess must also.

 

[Chugach]

Just as a reality check, assume that a falling bullet can reach at least the same terminal velocity that a skydiver in tuck position can reach: 200 MPH. Now, convert to fps:

200 mi/hr x 1 hr/3600 seconds x 5280 ft/mi = 293.3 fps

[This sounds about right...60 MPH is equivalent to 88 fps, so 200 MPH is roughly 3 times 60 MPH or about 3 x 88 = 264 fps.]

Don't know about anyone else, but I don't want to be hit by ...anything at even the pokey speed of ~300 fps.

What speed in fps does a decent paintball gun launch a (semi-solid) paintball at? Ever been hit at close range by a frozen paintball?