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Hey all, I have a question.

Let's say I am standing at the top of a tower launching a projectile down towards something on the ground I don't know, say 140 meters away (or any distance really). Is there any case where I might have to aim *slightly* lower than the target to hit it?

Could I possibly aim dead-on the target and overshoot? Assume the launcher is properly calibrated.

Not unless you live on some backwards planet where gravity is reversed.

To aim dead on and hit requires knowledge of the speed, angle, and destination of the traveling projectile.

I dont understand what u are talking about

If you're not talking about a propelled projectile, it should move in a parabola, so it depends on the range, but at the range of 140 meters every projectile should be going straight

let me explain

^Err...I dont think that would b the outcome.

Well normally when a projectile is traveling through the air, it has a spin to it. Either because of a rifled barrel that causes it to spin, or if it's a smooth barrel, the projectile might spin and flip kind of like a football does if you don't put a spin on it when you throw it.

That spin (especially on a rifled bullet, can cause the bullet to drift to one side or the other slightly, so you might need to aim slightly to the other side to adjust. That adjustment might be really small, but it is there. The longer the distance, the more it would travel to the side.

It would make sense to me that if that spin makes the projectile drift slightly to the side, it could also have somewhat of an upward force. Not enough to completely negate gravity, but possibly enough to "slow" gravity ever so slightly and cause the projectile to kind of glide like a glider would, but much, much less.

In other words, could there be any upward force at all on the projectile like there is to the side?

Am I making any sense? Check this out. This quote is taken from the exteriorballistics.com site [url]"http://www.exteriorballistics.com/ebexplained/5th/43.cfm"[/url]

I didn't follow University like physics law classes but if you shoot something (even a bullet) it will be drawn to the ground so if you use a rifle over like 140 meters you can hit right at the target, but if its over a few km then you gotta aim above.

Or something like that >.<' *sleepy*

go to sniper school

I don't think there would be a force against Gravity.

You mean:
-------^
-------|
-------|
------<=>------->
-------|
-------|
-------|
-------|
-------|
-------V

Well, it would look more like this:


------<=>------->
-------|
-------|
-------|
-------V

iirc there is no upward force when shooting a bullet. It really looks more like a curve (downward), but the curve isn't noticeable (in the beginning) because of speed. Anyhoo, "NEI".

140m? what are you using?



Doesn't matter anyways. Any upward force would be countered by gravity and would keep going straight (or drop).

i think it would depend on what you launched the object with. a water balloon that you threw would have more gravity affecting it than a bullet would. so depending on what you used you would need to adjust how you launched it

/potheads explanation of physics.


note: if we see something on the news about people gettin blown up from some guy tossing grenades off a 140m heigh building we know why lol

Newton's second law of motion pl0x

What I will say is that the balloon has a bigger surface, it would be greatly affected by wind. Depending on the shape of a building (some buildings are built to cut through air and it creates a jetstream) and wind, the balloon could be pushed "up" and away from the target, meaning you would have to aim below it.

a vertical acceleration on an object has nothing to do with horizontal velocity.

In theory it should follow a perfect parabolic curve if you shoot something horizontally.



1) Any object is subjected by the gravitational field by the earth described by the following laws:




g = 9.81m/s²

As you can see any object will have the same falling speed if there isn't an resistance at a given time.


The horizontal curve is dependant off the speed of the object. Without a engine or something alike, you won't have an acceleration to make the whole thing easier.

Vx(t) = Vx0
Yx(t) = VxO*t + Xo.



Next step.

First you must realise that the vertical and horizontal movement are completely independent of each other. No matter how fast you shoot the bullet forward, it'll land at the exact same time as a dropped bullet (provided you've shot the bullet 100% horizontal, else it would've gotten a initial vertical speed and that would change the times).


Last step: calculating when and where the object will fall.

1) Find out when the object will hit the floor. Needed parameters: The height of the building and the initial vertical speed. Solve the 2nd equation in order to find 2 time values and discard the wrong one, I hope your maths are sufficient enough to do so.


2) Now you can solve the last equation, because you got the needed parameter, time.



Things get more complicated if you need to add air resistance to the equation or when you shoot the object not 100% horizontal, but this is the basic physics you'll need.

Instead of shooting from a tower, why not pose your question in terms of a target range?
Given that we negate all factors other than gravity and air resistance and further given that your sights are properly 'calibrated' for a known distance the answer is easier: no.

There's a lot of science that goes in to bullet trajectories and ballistic coefficients but if your basic question is simple in nature, there is no need to make it more complex. The most common error that would have your desired result would be incorrect estimate of distance. dom's answer about 'updraft' was qualified correctly when he said that a balloon would present more surface than a bullet.

In physics the term 'Ballistic Trajectory of a Projectile' specifically describes a path without taking anything except gravity in consideration. It gets more complicated when we introduce air resistance or drag. Specifically regarding guns (and I don't remember the exact terms) there are 4 types of "Ballistics" - Internal (including your example for spin), Transition or Exit Ballistics where the bullet at the end of the barrel overcomes pressures, Inflight Ballistics and Termination Ballistics (where the bullet penetrates the target). Our definitions broaden yet again when we consider Ballistics itself which includes all objects and methods of propulsion. I could imagine myself on Jupiter and further imagine the moons in alignment but the gravity of that giant planet could not be overcome so easily; Roche's Limit would apply. But if your question is "While on the planet earth... and given reasonable simplification..."

There is such a thing in baseball. Putting an upward spin on the ball allows a pitcher to throw a 'floater' that does not sink the same as the more 'normal' pitches. It is characterized as much slower and higher than normal - considered a 'junk pitch' - sometimes the 'lob' is thrown with an upwards spin as it comes off the fingertips.

Youtube Eephus Pitches beneath Spoiler:

I understand all that. This all just came from a conversation I was having with someone and I'm trying to prove them wrong. Of course, if I stand on a tower and throw a paper airplane down at a -45 degree angle, it will not travel at a -45 degree angle the whole way. It also won't travel in a curve towards earth. It would catch some air and get some lift as it falls toward earth.

In a vacuum, I would think the object, whether paper airplane, water balloon, .45 caliber bullet, cannon ball, or grenade, would follow the same curve when it is thrown from a -45 degree angle towards earth.

When you add air, wind, maybe even atmospheric pressures, to the equation, those should all have an effect fighting against gravity. Those forces may be small, but are they not still there even from a grenade launcher or a cannon?

The website I linked to above might explain it better.



Yes, ballistics says the projectile should follow the curved line, but air resistance and other factors could make it follow a curve more in between the two lines in that graphic.

Yeah, I just assume the vacuum. >_>
afaik updraft would "fight" against gravity. "Catch the wind."

Ew physics =( its making my breakfast taste bad. I dont meant to spam but I'm sooo outta this thread.

...
physics >_> its not for woman.

Yeah most people do. I just don't know if the other variables are enough to make any difference, even by a fraction of a degree.

Think of a plane.

Plane are complicated.
Stupid curved wings lead to a lift or something.

I never liked physics and I only understood the mere basics like falling objects.

Probably be a bit more like:

<=>----------------------------------------------------------------------------------------------->
---|
---V

Exactly. I used the example of a glider and a paper airplane above since they are not self propelled. If you throw a paper airplane down at something, you can't just "aim slightly high".

I guess I just have to get my hands on a nice shiny weapon and a tall tower to test this out. (just kidding).

A bullet wouldn't have the same lift (if any) because it's made to "cut" the air.

Yes this is true, but what about something a little less "air cutting" like a grenade from a grenade launcher? Fire that at a quarter 140 meters away.

Well in the case of a grenade, it won't matter if you miss by a foot or two. As they say, close enough only counts in horse shoes, hand grenades, and other military explosives.

Unless you're trying to fire through a small hole at a certain range. You don't want to fire too high or too low and hit the wall instead of the hole.

Shoot a couple of time and se how much you need to aim

So you are trying to win an argument about this and would like a scenario where all factors are possible? Something where your "projectile" when properly aimed at a target would require you to 'overshoot' or 'aim low' to be able to hit your target?

Get a parachute or a wing glider. Jump from your tower and let the updraft carry you -- if you jump out at a 90° angle and went twice the distance you could easily show that a -45° angle (aiming low) was needed. Given the right conditions you could circle the target until you died from thirst.

The point that I tried to make above was that there are specific definitions in physics for reason. But if all you wanted was to win the argument you should try the ol' methods. Just say, "Uh-huh, would too, I'm right and you're wrong 'cause my daddy's bigger than yours." Or failing that just whip it out and show you're the bigger man. Hitting the target with your pee from the tower would probably prove your point to any reasonable person.

Isn't there a just released movie about this? Some kind of Matrix knockoff?

Well the debate deals with ammunition projectiles, not "pee" projectiles I guess it's not that important, just getting other people's opinions on it.

At least this page, http://www.exteriorballistics.com/ebexplained/5th/43.cfm, seems to support me when it talks about upward force Flift.

I'll weigh in on this when I get off work.