Does Firing a Bullet Upwards Have the Same Impact as Point Blank?

[jonnylane]

ahem.

negative attitude? Uh, no.

I know that the penetration depth is proportional to the sqaure of the velocity. I was just making the point that the depth just depends on the velocity (and the mass of course), but it came out wrong because I wasn't really thinking.

Despite having a degree (a british one), my inability to teach is evident. I will stick to those things that I am expert in, and try to avoid things I haven't studied in at least 5 years.

By the way, I admire the effort you put into the post before last. Bold text is the way forward in humiliation and making sure you are undoubtably right. Must have taken ages.

Jonathan

Oh, and the air resistance thing. Fine; learn kinematics, but don't expect to be able to answer a question like this without digging deeper into complexity. If we could ignore air resistance, my car would be cheaper to run (apart from the cooling issue) and parachuting would be nothing short of suicide.

And why not give a numerical answer? Precisely for the reason above. Why work to get what is ultimately a wrong answer? To realize understanding of an impossible situation.

 

[jpritch]

You would have the same result if the terminal velocity of the bullet was equal to the velocity of the bullet as it comes out
of the gun barrel.
I don't believe that the terminal velocity could equal or exceed that of the initial velocity out of the gun barrel.
That can be determined by finding the velocity that the bullet reaches when the acceleration reaches zero while falling.
Then compare that velocity with the initial velocity of the bullet when it leaves the gun barrel.
For a falling object, the force acting on it is gravity and once that object reaches its terminal velocity it will no longer gain speed.

 

[Adrian Baker]

I'm glad that this thread was just a "Simple question about gravity and force..."

I'd hate to see the discussion if it were a difficult one!

 

[jammieg]

It makes sense but has anyone ever experimented with it scientifically? I mean with very exact mearsurements and in a vacuum and not with a bullet of course? What would it mean if the return force or terminal velocity turned out to be slightly greater than expected?

 

[chroot]

Originally posted by jammieg
It makes sense but has anyone ever experimented with it scientifically? I mean with very exact mearsurements and in a vacuum and not with a bullet of course? What would it mean if the return force or terminal velocity turned out to be slightly greater than expected?

Of course it's been tested in a vacuum.

If the projectile didn't come down with the same kinetic energy it had when it was fired, it would mean energy is not conserved, and pretty much everything theory in physics would fall apart. Literally.

- Warren

 

[krab]

...has anyone ever experimented with it scientifically? I mean with very exact mearsurements and in a vacuum and not with a bullet of course?

What would it mean if the return force or terminal velocity turned out to be slightly greater than expected?

The usual definition of terminal velocity is the fastest a body falls. In a vacuum, this is infinite. Read the complete thread.

If you mean by "terminal velocity" the final velocity, then the answer to your question is it would mean that energy is not conserved.

 

[jpritch]

I agree with krab

In a vacuum you would not have air resistance to slow the bullet which would result in a terminal velocity. Terminal velocity only occurs when you are NOT in a vacuum.

 

[jammieg]

Here's a fun page dealing with dropping balls and terminal velocities:
http://www.explorescience.com/activities/Activity_page.cfm?ActivityID=27

 

[Mr. Robin Parsons]

Lets see, I used to have a .22 cal rifle, and on the boxes of cartridges it indicated that the muzzle velocity of the bullet was about 1200 ft/sec, ~1 mile in about 4.2~4.5 sec so it order for it to have the same velocity in it's freefall back towards the ground, it must be able to achieve this kind of speed.
I would respectfully suggest that if you do actually do the Air resistance figuring, (add in the fact that it is no longer given the lovely "spin" on it, that the rifleing(sp?) inside the barrel gave it, to assist/enhance it's ability to penetrate the atmosphere) you will find that it cannot achieve this velocity.

 

[pmb]

Originally posted by Oliva
I'm hoping you can help. My husband and I have been discussing a situation and we would love to find an answer. Any direction you can give me would be great. (Please note, I haven't taken a physics class in about 15 years)

If you shot someone in the head with a gun at point blank range and you shot the same gun straight up into the air and the bullet came down and hit the person on the head would you be shooting this person with the same amount of force and/or speed?

This is a lot to read through so please forgive me if I'm repeating anything that was already posted.

First off - when the bullet leaves the gun it has a certain amount of energy. At point blank range the energy is about the same was when it left the gun as when it hits the target. The further away the gun is from the target the more air it has to go through. The more air it goes through the more energy is dissipated and thus the slower it will be going. Shooting it straight up means that it has to travel through a lot of air and when it comes down it will reach a terminal speed which is much less than the muzzle veclocity. However if you did this in the absense of air then it would hit with the exact same speed since no energy would be lost to the air.

Pete

 

[haynewp]

I used to go bird hunting with my friend when I was about 16. He would fire his shotgun directly up in the air when we we standing close and then the pellets would land on us. He would call this "getting sprinkled". Those shotgun pellets must have a low terminal velocity, we never were injured.

 

[Vector 9]

Final answer

I'm hoping you can help. My husband and I have been discussing a situation and we would love to find an answer. Any direction you can give me would be great. (Please note, I haven't taken a physics class in about 15 years)

If you shot someone in the head with a gun at point blank range and you shot the same gun straight up into the air and the bullet came down and hit the person on the head would you be shooting this person with the same amount of force and/or speed?

I was directed to this thread to provide an accurate answer to this question.

The falling bullet would in no way have the force of the one fired at point-blank range.

The moment the bullet is fired straight up it is acted upon by both gravity and air resistance. The moment it stops and begins to fall, again it is acted upon by both gravity and air resistance.

It is true that people have been killed by falling bullets. It is most likely that the majority of those were the result of being fired at an upward angle, causing reduction in bullet speed/force, yet maintaining significantly more than if it were fired straight up.

We know gravity is represented as 32 feet per square second but, the air resistance would never allow the bullet to reach the same velocity as if it had been fired. The air resistance is represented as the coefficient of drag times one half the air density times the velocity squared, times a reference area on which the drag coefficient is based. You won't be firing out of the troposphere so the air resistance is not a factor. The coefficient of drag for a stabilized bullet is approximately .295. In short the bullet does have a terminal velocity, and the importance of drag cannot be overemphasized.

I prefer real-life experiments.

Drag
Out of a rifle firing a .30-06 FMJ 150 grain (.021 pounds) bullet horizontally, we show a muzzle velocity (point-blank) of 2910 feet per second, and carrying 2820 foot-pounds of force. At 100 yards that same bullet drops to 2696 fps and 2421 foot-pounds of force, and at 500 that same bullet drops to 1934 fps and 1246 foot-pounds.

The reduction of velocity and force is due to the air resistance alone, and keep in mind that the bullet is stabilized by the weapon's rifling and is not tumbling.

Now, we fire that bullet straight up, it stops as gravity and air resistance overcome the muzzle velocity, and it falls. The height is actually irrelevant if the bullet is allowed to have over 10 seconds of fall time as the falling bullet will obtain its terminal velocity of approximately 300 fps in just under ten seconds. At impact it will exert just over 30 foot-pounds of force. It is still technically possible that a 150 grain bullet at 300 fps can still cause great bodily injury or death but it is .01 the force of a point-blank shot.


For additional information see:
"Remmington Arms Ballistic Charts"
"Official Report of Vertical Time Flight for Small Arms Ammunition"

 

[futb0l]

just remember that

Force = Mass * Acceleration

which means that when the bullet is shot up it looses acceleration through the air resistance.

 

[gunblaze]

I'm hoping you can help. My husband and I have been discussing a situation and we would love to find an answer. Any direction you can give me would be great. (Please note, I haven't taken a physics class in about 15 years)

If you shot someone in the head with a gun at point blank range and you shot the same gun straight up into the air and the bullet came down and hit the person on the head would you be shooting this person with the same amount of force and/or speed?

I personally feel that the bullet's power/force will all be used up during its movement upwards! then when it's power, when it is moving up, is used up, it will start moving down!
A bullet is very small so the pull of gravity on it is very small .Plus the air resistance, the force the bullet applies shouldn't be too great!

 

[Loren Booda]

gunblaze,

Remember Galileo's experiments showing equal gravitational acceleration for substantially different masses?

The bullet's momentum will decrease somewhat due to friction with and buoyancy in the atmosphere.

Read some of the other posts.

 

[Alkatran]

I can't believe some of the things I've read here.

We have people saying incredibly foolish things (which we learned about in... grade 11) and other people going to great lengths to show them their errors.

Can't we just say the bullet's going to be going slower than point blank but will still have the potential to kill (way too many variables (head shot? type of gun? bullet? weather?) to determine a kill or not).

 

[gunblaze]

Can't we just say the bullet's going to be going slower than point blank but will still have the potential to kill (way too many variables (head shot? type of gun? bullet? weather?) to determine a kill or not).

Well... I dun think so.

A bullet NOT shot from point blank would never kill!(no matter the type of gun used)

U dun die from a bird **** from the sky, do u?

It is the same... All kinds of bullet r light!(i presume)

The bullet when its fall from the sky will have already loss all its force by the gun...so the power the bullet have will just be from the downward movement of the bullet, and not plus the force accumalated from the upward force!
considering the pull of gravity on that bullet minus the resistance from the air, without doubt the resultant force would just be as small as a stone.

(We can take it that the bullet is just another lightweight item free-falling from the sky.Not a bullet from a gun anymore)

 

[Alkatran]

Bird poop isn't made out of metal (it is much less dense), and probably tends to spread out a bit on impact, reducing stress. A bullet shot in the air probably goes higher than your average sea gull ;) .

Also, you need to remember that it doesn't matter where a force comes from, only the total force supplied matters (impulsion?).

You say bullets are light, they are also very small. This means they don't need to be going incredible speeds to penetrate.

 

[gunblaze]

hmmm...i think i get what u mean!

Also, you need to remember that it doesn't matter where a force comes from, only the total force supplied matters (impulsion?).

But i still dun understand the above...can u further elaborate?

 

[Loren Booda]

Ever warned not to drop pennies from a tall building?

 

[TeV]

Can't we just say the bullet's going to be going slower than point blank but will still have the potential to kill (way too many variables (head shot? type of gun? bullet? weather?) to determine a kill or not).

Bullet will be definitely slower when it returns becouse of the air resistance.But is it harmless?I think not.Besides,ballistics will tell you the situation is quite nonlinear,bullet is usually fired with high axial rotating velocity in order to be steady during the flight and other reasons.
It wouldn't surprise me that inital trajectory angle of 1° become as large as 10° when it comes down due to the effects.
Bear in mind that 10 g rock can produce serious injure to the victim when dropped from the high skyscraper.If the bullet is pointy and person is unlucky..