I was reading your section on sniper ammunition. It was informative and incorrect in places. Bullets shot straight up in the air decelerate at -9.81 meters per second squared with added air resistance which will be the same on its return trip to earth. When it reaches its apex it will begin to accelerate toward earth at 9.81 meters per second squared with the same air resistance. So, you will see that its trip up is exactly equal to its return trip to earth. Not 17 seconds up and 45 seconds as you stated.

-- NotA Bloney Eater (UrfullOshit@yahoo.com), February 12, 2003

Answers

There is very detailed information at: http://www.loadammo.com/Topics/March01.htm

If this link doesn't work, here's the short story. After firing 500 rounds vertically, and timing their descents, the Army stated that the .30 caliber rounds went up at 2700 feet per second (1840 miles per hour), returned to Earth, and hit their platform at 300 feet per second (205 miles per hour).

Other tests determined that the terminal velocity of a .30 caliber round is 320 fps, or 218 mph.

My 2 cents: If you go 2 times faster, you have 4 times the air drag. If you go 3 times faster, you have 9 times the air drag. However, in your car, if you want to go 2 times faster, you need 6 times the horsepower.

-- Curtis Tricarico (curttric@prodigy.net), November 09, 2003.

Air resistance robs the bullet of energy in both directions. As the bullet goes up it loses energy to friction (w=f*d= change in energy) so at the top it has lost some energy and what is left is stored as energy potential. If you could magically turn off air resistance at this point and drop the object it would not reach its original velocity at its starting point. It actually gets worse as we turn on air resistance again and we lose more energy on the way down. Even though gravity is accelerating the object, wind resistance takes away from its potential speed, not increasing it faster than gravity would on its own. What you end up with is a bullet travelling slower at its starting point then when it was originally fired.

-- Dean Turchansky (dturchan@telusplanet.net), October 07, 2003.

The statement in the original question disregards the important fact that the air resistance force and the gravity force are acting in the same direction as the bullet goes up. In the upward direction these two forces add together in oposition to the gun induced bullet's momentum.

This is the situation of two forces trying to stop an object which was already in motion. On the way down however air resistance and gravity oppose each other as the bullet tries to gain momentum induced gravity. The resistance force is a function of the downward speed and when it becomes equal to the pull of gravity there will be no net force acting on the bullet and thereforce acceleration is zero At this point the bullet reached terminal velocity which remains constant as it comes to ground.

These are two totally different situations.

-- Alberto Rodriguez Llado (alberto@prdigital.com), July 24, 2003.

For a vacuum, you would be right. In air, there is this thing called "terminal velocity" which means that the falling bullet will not go above a certain speed because the air-resistance is equal to the pull of gravity (air resistence is speed-dependent). Therefore if you shoot a bullet straight up at a speed greater than terminal velocity, it will still come down with at most the terminal velocity. On the way down it will accelerate for a while but then maintains a constant speed.

-- Marco (none@none.com), June 13, 2003.

No, you havent learnt real life physics. after the book this is correct but you forget one thing, there is a limit for the speed in freefall. the bullet goes up with a speed around 500 - 900 meters per second and begins to decelerate at -9.81 as you said and when it goes down it does the thing you said but just first. the air resistance will work up while the speed get more. so after a while the bullet can't go faster, because there is a balance between the airspeed and air resistance. and tha max speed is lot lower than the mussel velocity, so this information is correct, a bullet that goes faster up than down will be longer on the downway than on the way up.

Sorry for bad English. But there are also wannabe snipers in Iceland...

-- Magnus Ragnarsson (magnus@xtec.is), February 14, 2003.