Bullets shot into the air.

knockon

Watching this insane practice of shooting rounds into the sky on the Nightly News has prompted a buddy of mine to ask about trajectory and other science stuff. If its fired directly at 90 deg, how high does it go before gravity takes over...etc Anyone? We all know it's dangerous and illegal here but purely scientific.

deerhunter1

knockon wrote: »

Watching this insane practice of shooting rounds into the sky on the Nightly News has prompted a buddy of mine to ask about trajectory and other science stuff. If its fired directly at 90 deg, how high does it go before gravity takes over...etc Anyone? We all know it's dangerous and illegal here but purely scientific.

probably depends on weight, velocity, etc and any other factors

Cass

I'm sure there is a scientific way to calculate the MV, caliber, effect of gravity, etc, but actually doing it, i couldn't see it. Would you want to be in a helicopter or something similar when people below are firing upward?

Secondly, depending on caliber, BC, etc different bullets will perform differently. Mythbusters done a somewhat similar test a while ago and on a relatively calm day the round, fired at 90 deg straight up, still traveled 100's of metres away from the point in which it was fired.

Have a look here. As you said though its purely academic. Any attempt should be met with a swift slap to the head.:cool:

Grizzly 45

The Bagdad[or whatever current Middle East hotspot] unload!!Point weapon at angle of 80 to 90 degrees.Set on full auto,pull trigger until mag is empty!
When Bulgaria finally fell to democracy,and the citzens looted their army barracks ,there were ove 60 deaths around Sofia within a 48 hour period from that kind of carry on in the crowds.The actual riot police and army didnt kill anyone apprently!!:eek:

Offy

knockon wrote: »

Watching this insane practice of shooting rounds into the sky on the Nightly News has prompted a buddy of mine to ask about trajectory and other science stuff. If its fired directly at 90 deg, how high does it go before gravity takes over...etc Anyone? We all know it's dangerous and illegal here but purely scientific.

A lot of factors have to be taken into account, the starting speed (normally=0), the final speed, the acceleration, wind factor, gravity, etc.
There are engineering calculations used to work this out.
Have a look at these sites:
http://www.ajdesigner.com/phpprojectilemotion/vertical_velocity_equation.php
http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Projectiles/ProjectileIntro.html
http://zonalandeducation.com/mstm/physics/mechanics/curvedMotion/projectileMotion/generalSolution/generalSolution.html
http://staff.hartdistrict.org/glyle/tools/proj_mot_how_to/proj_mot_how_to.htm

FISMA

Gravity acts on the bullet equally throughout its entire flight. From the instant the bullet clears the barrel to the instant it is just touching the ground, gravity is accelerating the bullet at 9.80m/s every second.

The gravitational Force does depend upon separation distance. However, the bullet will not get high enough for this to be a meaningful/measurable factor. Astronauts in low earth orbit still weigh about 90% what they would on Earth.

Once the bullet is fired, perpendicularly, it is no longer rotating with the Earth. Hence, it will not land in the same spot.

The biggest concern is air resistance. Air resistance is a major factor and probably is proportional to the square or cube of speed.

Unlike acceleration due to gravity, air resistance depends upon how fast you are going. On the way up the bullet has a high average speed and on the way down it has a lower average speed. This is why it takes more time for the bullet to come down from the top than to get to the top.

Friction is always doing work to take energy (in this case Kinetic) away from the bullet. Being a non-conservative Force it does not give back what it takes away. This is totally different from Gravity, a conservative Force. On the way up gravity slows you down but on the way back down it speeds you up. You won't get back to the muzzle velocity because of the work done by air resistance.

Also, I am unconvinced that a bullet falling at terminal velocity would kill someone. Obviously, reckless and stupid to try, but terminal velocity of a bullet should be quite low, 100kph? Even considering the small probability of being hit by a stray shot, that's not in the lethal range.

4gun

didn't Mythbusters do a show on it a couple of seasons back wind will always cause drift

garv123

i saw it tested on a episode of mythbusters i saw recently.
they fired different caliber guns up into the air and found where it landed. the handguns weren't fatal coming down and i dont think any of the rifles were either.
they said though that even if the gun is only a few degrees off perpendicular to the ground the bullet can keep its velocity and still be fatal at miles away


BUT thats mythbusters:rolleyes::rolleyes:

garv123

just did a google search

Bullets fired into the air maintain their lethal capability when they eventually fall back down.
BUSTED / PLAUSIBLE / CONFIRMED
In the case of a bullet fired at a precisely vertical angle (something extremely difficult for a human being to duplicate), the bullet would tumble, lose its spin, and fall at a much slower speed due to terminal velocity and is therefore rendered less than lethal on impact. However, if a bullet is fired upward at a non-vertical angle (a far more probable possibility), it will maintain its spin and will reach a high enough speed to be lethal on impact. Because of this potentiality, firing a gun into the air is illegal in most states, and even in the states that it is legal, it is not recommended by the police. Also the MythBusters were able to identify two people who had been injured by falling bullets, one of them fatally injured. To date, this is the only myth to receive all three ratings at the same time.

FISMA

Big bore shooters must be especially vigilant to ensure they do not overshoot their target.

I was told that 303's and 30-06's could be lethal, at shallow angles, up to 6 miles away.

Kind of humbling.

Longranger

I've read up on this before and from what I can remember,a .22 bullet fired at an exact 90 degree angle would hit the ground on the way down at about 125 fps. A .308 would hit at about 200 fps. Bullet mass would be a major factor regarding lethality but apparently the .22 would give you a nasty gash on the head but the .308 could kill you depending on where it hit your head. The angle is crucial,90 degrees exactly and the bullet looses its spin quicker,therefore slowing down quicker. Also,it would probably hit you tail end first because this is the heaviest end. On the other hand,a bullet fired at,say 80 degrees would not simply rise,stop and fall,but would travel in an arc and not come to a dead stop,then drop,so it would not lose nearly as much velocity. Chances are, the bullet fired even just off the vertical would probably kill you but anyone who wants to find out is welcome to try as long as they're in a different county to me!

pedroeibar1

FISMA wrote: »

Gravity acts on the bullet equally throughout its entire flight. From the instant the bullet clears the barrel to the instant it is just touching the ground, gravity is accelerating the bullet at 9.80m/s every second.

No. Gravitational force is pulling back the bullet after it leaves the barrel.

FISMA wrote: »

.....................................Also, I am unconvinced that a bullet falling at terminal velocity would kill someone. Obviously, reckless and stupid to try, but terminal velocity of a bullet should be quite low, 100kph? Even considering the small probability of being hit by a stray shot, that's not in the lethal range.

At its apex, the bullet stops, force spent, gravity takes over fully and it falls back to earth accelerating at 32 ft per sec per sec, until the air resistance halts it at its terminal velocity, probably about 120MPH.
P.
(Waiting for the paper-punchers to get their TI calcs on the job.:p )

unfortunately

FISMA wrote: »

Once the bullet is fired, perpendicularly, it is no longer rotating with the Earth. Hence, it will not land in the same spot.

This is false. There is no such thing as absolute motion. For example, if you were on a ship traveling north at 16 knots and threw a tennis ball directly up into the air, where would it land? Aristotelian physics says that the ship moves under the ball and so it would land away from where you are standing. But in reality it lands back down where you're standing (ignoring the effects of wind). All motion is relative.

This applies to a rotating earth as well as argued by Galileo.
http://en.wikipedia.org/wiki/Galileo's_ship

Kinda makes sense otherwise imagine trying to pour a drink on the deck of a ship, once the liquid leaves the bottle in is in the air and is no longer traveling with the ship, hence you would have to hold the glass away from under the bottle to avoid spillage!

FISMA

Peace Peroeibar!

D'oh - epic fail on my behalf. I stand corrected.

I did not mean to write, although I did, that the bullet is always accelerating (unless in a vacuum), it does indeed hit terminal velocity at some time on the way down, hence accel = 0.

The Force of Gravity is point dependent. However, the acceleration due to gravity is not, since we have air resistance.

<edit>The following sounded a bit antagonistic after a re-read, it is not meant to be, sorry if it comes off that way.<end-edit>

pedroeibar1 wrote: »

At its apex, the bullet stops,

The bullet stops? With respect to what? An Earth bound reference frame?

This is not the case when you have a reference frame, attached to an Earth that is accelerating. The projectile, will lag the reference frame and follow a parabolic path.

pedroeibar1 wrote: »

..., gravity takes over fully ...

Was this a colloquial statement? You do not mean this literally, do you? Are you talking about the Force of Gravity or the acceleration due to gravity? At what time or place was the Force of Gravity not fully acting on the mass?

A round fired straight up on an Earth that was not rotating (assuming no accelerations due to winds) would be at rest at the topmost point.

However, at that instant it would be accelerating at the local value of acceleration due to gravity, which would not be 9.80m/s/s, but close enough to it. It would then begin to speed up with decreasing acceleration until it asymptotically reached terminal velocity.

unfortunately wrote: »

... if you were on a ship traveling north at 16 knots and threw a tennis ball directly up into the air, where would it land? Aristotelian physics says that the ship moves under the ball and so it would land away from where you are standing. But in reality it lands back down where you're standing (ignoring the effects of wind). All motion is relative.

unfortunately, you forgot to tell us one key point. Is the ship accelerating or not? If it is accelerating, then the projectile will trail the lift off point, if in motion with a constant speed, it will go straight up and down. The Earth is most definitely accelerating.

But please do not take my word for it.

If you have not already seen this Physics classic - Frames of Reference, have a look at youtube.

If you do not have the time, go to 5:00

https://www.youtube.com/watch?v=dAoGpflOmdw

Last edit...

pedroeibar1 wrote: »

(Waiting for the paper-punchers to get their TI calcs on the job. )

C'mon now Pedroeibar, True geeks wouldn't be caught dead with anything less than an HP in the pocket of their short sleeve shirt! Reverse Polish Notation Forever!!!

unfortunately

FISMA wrote: »

unfortunately, you forgot to tell us one key point. Is the ship accelerating or not? If it is accelerating, then the projectile will trail the lift off point, if in motion with a constant speed, it will go straight up and down. The Earth is most definitely accelerating.

Ahh, I see.

But just to see if I am understanding this; assume that the atmosphere rotated with the earth - then the bullet would fall directly down?

But I understand that in reality the deflection of the bullet due to Coriolis effect would be very small.

Double Barrel

I should be asleep.
Have fun: http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html

Sparks

unfortunately wrote: »

But I understand that in reality the deflection of the bullet due to Coriolis effect would be very small.

Negligible. It always is w.r.t. rounds fired, except at extremely long ranges (1km and up) and even then, it's tiny - you're talking an inch or three of deflection in total, far far far less than you'd get from any number of other factors.