When a bullet is fired vertically (upwards),?

Question

it will return back down right? I just had a test at my school about these thing and a question popped up in my head, if the bullet comes down, it will have a high velocity right? Can it hurt someone as bad as a bullet fired directly at the person?

My guess is no, because air friction won't make the bullet as fast.

Please explain what would actually happen and correct me if I'm wrong...

Answer 1

Link below has detailed answer to your question.

For your convenience, I have copy-pasted the discussion given in the link.

Grandpa -

My friends and I have been debating about what happens when you fire a gun straight up in the air. Some of us think the bullet will come down as fast as it went up, and others think it's safe when it comes down. Can you help us settle this. The Fourth of July is coming soon.

- Thanks - Kimberly



Kimberly -

Different guns have different "muzzle velocities." That's the speed that the bullet is going when it leaves the barrel. Many high-powered rifles have muzzle velocities that are 3000 feet per second or more. That's more than 2000 miles per hour.

When such a gun is fired straight up into the air, this is what happens:

The bullet leaves the gun at 3000 feet per second. There are two things now that slow the bullet down as it goes up. One is gravity - which slows the bullet 32 feet per second every second. If this were all that slowed it down, then after 10 seconds, the bullet would still be going (3000 - 320), or 2680 feet per second. This is not even close to the true velocity after 10 seconds, because air friction is slowing the bullet also. That friction is much greater while the bullet is going fast. In the first second, it may slow the bullet by 1000 feet per second. Then in the second second, maybe another 500, and then less and less, until finally, the gravitational slowing is more significant than the friction. The bullet will continue to slow down until it stops at the top.

Now let's talk about when the bullet heads back down:

The same two forces are present, but now the gravity part is speeding up the bullet - friction is still trying to slow it down. Gravity will be speeding up the bullet 32 feet per second every second, but friction will be increasing more and more as the bullet speeds up, and this friction will subtract from that 32. There is a certain velocity when the friction is equal to the gravity in the opposite direction. At this point, the frictional acceleration is 32 feet per second every second upward (or -32), while the gravitational acceleration is 32 feet per second every second downward (+32). From now on, the bullet will have no acceleration at all (32 - 32 = 0). When this happens, the velocity of the bullet is called its "terminal velocity." The bullet will continue at the same velocity until it hits the ground or some object.

This terminal velocity is different depending mostly on two things. 1. The density of the thing that is falling. 2. The shape of the thing that is falling. Bullets are very dense (usually lead), and they have a shape to allow relatively low friction. The terminal velocity of a feather may be only 2 feet per second because of its shape and density, but the terminal velocity of a bullet could be 300 or 400 feet per second. This could be about 300 miles per hour.

Now about your debate:

1. That 400 feet per second is much slower than the 3000 feet per second that the bullet had when first fired. If you or a friend argued that the bullet is going slower on the way down, then you or that friend was correct on the physics.

2. It is still dangerous. A three hundred mile per hour piece of lead can still do harm. There is no question that it is not as effective as a bullet fired directly at something. The bullet that is fired at something has another very important feature, however, a feature the bullet fired into the air does not have. It was aimed - there was an intended target. The bullet fired into the air falls randomly and could hit anything. If it hit someone right on top of the head, it's possible that it could kill. It's going about three times as fast as a professionally hit tennis serve, and it's much smaller than a tennis ball, and harder - more penetrating. When you triple the speed, the energy goes up nine times (it's proportional to the square of the speed), and I'll bet there's no-one who wants to be hit by a tennis ball with nine times the energy of a fast serve. Then, because the bullet is small and hard, it is hundreds of times more penetrating than that tennis ball would be. Put a tennis ball in your palm and put twenty pounds on top of it. No problem. But now put the blade of a screw-driver on your palm and put twenty pounds on that. That will hurt. Same twenty pounds - smaller cross section - more penetrating. If you or a friend argued that the falling bullet is dangerous, then you or that friend was correct on that.

3. Ultimate winner of the debate:

If you or a friend argued that the bullet falls much slower than the muzzle velocity, is still dangerous, but not as dangerous, then you or that friend won the debate and had everything right.



Bottom line: Grandpa does not recommend firing guns straight up into the air, but he would rather have a hundred of these than just one aimed and fired at him. Guns are particularly dangerous in our country, because we take them far too much for granted. They are familiar to us, and we have too much comfort concerning them. They are often treated as toys. Sometimes very large children play with them.



Note: If this gun were fired into a vacuum - no air - then the bullet would fall to the same speed as it left the muzzle. Many times in physics classes, friction is ignored. This is because the problems become much more difficult when friction is included, and the principles can be taught easier with this assumption. The assumption is, of course, false. When we do real physics in the real world, we cannot ignore friction. Our results would be ridiculous. For example, in this vacuum, the feather would fall as fast as the bullet. You would be very surprised on the moon if you held a feather in one hand and a rock in the other and then dropped them at the same time. Both would hit the ground together. Though Grandpa would expect this result, it would still be a surprise to see it.



- Grandpa

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Answer 2

When a bullet is fired upwards it leaves the muzzle of a gun it has a very high velocity. The frictional forces acting on a body would be very high if its velocity is very high. So when the bullet leaves the gun at a high speed it experiences a lot of retardation(the friction plus the gravitation.) So when the bullet eventually stops due to friction the height achieved by the bullet would be less comparing when it is fired in vacuum. So if the height gained by the bullet is reduced the speed by which it turns would be reduced. So the kinetic energy of the bullet would be reduced. So it would do less damage as compared to a bullet fired straight at a body. But it would still have enough velocity to kill a person if it falls directly at his\her head. But now if we find the probability of the bullet falling on the head would be very less. The probability you firing the bullet at 90 degree is very less even if you change the angle by 1 degree the path of the bullet will be changed it might fall 20 meters away from you so you have to be really accurate if you want to get the bullet fall straight at your head. Which is not advisable.

Answer 3

yes the bullet will come back down

and yes, such bullets, when coming down, can be very dangerous, and kill. This is actually a common occurrence in those countries where people are a bit too trigger happy to celebrate anything by shooting their AK-47's towards the sku.


of course, due to air resistance, the bullets will generally come down slower, than the original muzzle speed.
On your average military rifle, the muzzle speed of the bullet is about 700-750 meters per second (2'300 to 2'500 ft / sec, or 1'580 to 1'690 mph).
Whereas when coming down, the bullet can maybe reach a max speed of 300 ft/sec (205mph, 91 m/s).

But even coming down 7 or 8 times slower, leaves enough energy to kill someone - 205mp is still a pretty serious speed after all


Hope this helps

Answer 4

As my ol' Man, a died-in the-wool rifle NUT explained it to me:

A bullet fired exactly vertically up in the air will lose velocity as it gains altitude, until it reaches 0, just as an aircraft does when it stalls in a vertical climb.
As the bullet returns to the ground, the ONLY velocity it will have is that imparted to it by the acceleration of gravity itself, or 32ft. per sec. squared, and NO MORE. This is called 'terminal velocity', about 120mph, or less than 200fps, and will even be slowed slightly by air resistance on descent.

It could possibly cause a wound,but we seriously doubt that it would be fatal. With only the speed imparted by gravity, it wouldn't be nearly as dangerous as a bullet fired directly at a person.

Answer 5

What goes up must, come down. When the bullet is fired, depending on the type of gun and caliber of bullet, it is shot at a certain speed. Eventually, it must come to a point, after reaching maximum height and stop. It then falls back to Earth. Whatever it strikes, animal or person, it can still kill with with devastating effects thanks to speed and gravity.

Ed: Take the example of guns being fired for New Year's Eve in any major city. There have been cases where people and kids have been struck and killed, blocks away from falling bullets.

Answer 6

It will come down with a high velocity but not as fast as it left the gun. True, air resistance does effect the bullet. More importantly, when the bullet falls back to earth, it's tumbling vice spinning like it does out of the rifled shaft of a gun. It's like the difference between throwing a football normally or throwing it end over end. The tumbling football will slow faster than the "normally thrown" football and impact its target slower.

Hope this helps.

Answer 7

Mythbusters did an episode on this. There have been instances where people actually died from a bullet fired in the air, but the Mythbusters were unable to prove that it would work. They have a website, not sure what it is, and they might have something on there about it.

Answer 8

bullet fired vertically

Answer 9

space shuttles and asteroids entering the earth will be affected by air friction because of its very high velocity. i think air friction that affect the bullet is low not only of its size, it yes has high velocity but not high enough. but it will not slow it down. it can still kill people if he was hit in a critical part like the head or heart. many people in the past years die here because of stray bullets..mostly in newyears eve where people fire their guns rather than fireworks

Answer 10

the friction in the air will slow it down but unless it hits a vulnerable part of the head you will be alright if an abulance is nearby
don't try it though because there is a 37% you'll be permanatly damaged