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Parabolic tajectory, hold under and hold over explained in very lame terms


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Hi lads and ladies,

 

I was going to put this into a DVD but when burnt to DVD quality it wasnt looking very good (picture wise) so here it is in HD.

 

For best picture watch in full screen at HD quality.

 

Its a very simple and easy way to understand parabolic trajectory and is how I teach my lads when instructing shooting and the characteristics of a bullet to ensure they understand it easily the first time.

 

 

Si

 

http://www.youtube.com/watch?v=QGUzQX2UcqM

Edited by zini
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Very good that Si,

 

Don't know if you may be able to help me out at some point I'm in the north of the county but would benefit probably from coming to see someone like yourself to ensure I get set up properly.

 

Let me know if you could maybe help us at some point.

 

Thanks for the very interesting video.

 

Liam

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Hi Falcon,

 

Yeah I normally just say trajectory but as it was for a demo I thought best use the correct terminology.

 

Hi Bill,

 

Thanks for the comment buddy.

 

Hi Liam,

 

Sure buddy Ill help anyone out shooting wise if I can.

 

You only live down the road from me mate as I’m in Nottingham so it shouldn’t be a problem.

 

Thanks Rik buddy.

 

Si

Edited by zini
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Si, great explanation of the hold under/over, and trajectory.

 

The only thing I'll say is that the trajectory curve is not parabolic. The angle of descent is steeper than the climb angle (vertical acceleration is constant whereas speed decreases downrange) whereas in a parabola the shape each side of the apex is the same. That makes no difference to the understanding of how the pellet behaves, which your explanation is most helpful on.

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Si, great explanation of the hold under/over, and trajectory.

 

The only thing I'll say is that the trajectory curve is not parabolic. The angle of descent is steeper than the climb angle (vertical acceleration is constant whereas speed decreases downrange) whereas in a parabola the shape each side of the apex is the same. That makes no difference to the understanding of how the pellet behaves, which your explanation is most helpful on.

 

Pedantic bugger!! :laugh: Ment in jest, Matt :thumbs::D

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Thanks Matt :thumbs: you are 100% correct in what you are saying buddy.

 

However I am too buddy as this is called the bullets parabolic trajectory (more common trajectory) whether not a true parabola or not mate. That or the year I spent studying ballistics someone was lying to me :laugh: .

 

Read this and it explains both what you said correct and what i said correct in more technical terms.

 

I didnt want to make things more technical than they needed to be for people on here. I cant see the point in trying to make things harder than they need to be :no: .

 

Projectile Trajectory

 

Definition: A projectile is a moving object that has only one force acting upon it: the force of gravity.

 

The path it follows is called its trajectory.

 

Projectiles travel with a parabolic trajectory because the force of gravity accelerates them downward from their otherwise straight-line, gravity-free trajectory. Neglecting air resistance, a projectile would maintain a constant horizontal velocity since there are no other horizontal forces acting on it. At the same time the downward force and acceleration results in a downward displacement from the position that the object would be if there were no gravity.

 

In other words, projectile motion has two components: horizontal and vertical, causing the trajectory of the projectile to curve. In the horizontal component, velocity is constant so it continues straight forward covering equal distances in equal times. At the same time, it is accelerating downward because of gravity, travelling larger downward distances in each successive time interval. These two simultaneous components create a curved path.

 

Bullet drop and parabolic trajectory

 

The effect of gravity on a projectile in flight is often referred to as bullet drop.

 

It is important to understand the effect of gravity when zeroing the sighting components of a gun.

 

To plan for bullet drop and compensate properly, one must understand parabolic shaped trajectories.

 

Due to the near parabolic shape of the projectile path, the line of sight or horizontal sighting plane will cross the projectiles trajectory at two points called the near zero and far zero in case the projectile starts its trajectory (slightly) inclined upward in relation to the sighting device horizontal plane, causing part of the bullet path to appear to rise above the horizontal sighting plane.

 

The distance at which the firearm is zeroed, and the vertical distance between the sighting device axis and barrel bore axis, determine the apparent severity of the "rise" in both the X and Y axes (how far above the horizontal sighting plane the rise goes, and over what distance it lasts).

 

For ayone who wants to really read about parabolic trajectory in the geekiest manner possible, read this and it explains parabolic trajectory in great detail.

 

http://www.worsleysc...trajectory.html

 

Hope this makes sense.

 

ATB

 

Si.

Edited by zini
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Good vid Si. Another interesting point which I think most people are aware of is that gravity is constant, and a few years back when running some of our courses we used to demonstrate this with a small piece of equipment, on a bench in the classroom, one of the lads had knocked up, years before.

What you had was 2 ball bearings (to represent bullets) and an elastic powered firing mechanism, that projected one of the balls. As that ball passed the second ball, the second ball was released, which just fell vertically as a result of gravity.

What amazed some of the students, was that no matter what the velocity of the first ball, both balls hit the ground at the same time. It is because of this fact, as you know, that elevation adjustments are always easier to calculate, than deflection adjustments.

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Pedant? Moi?

 

Lol.

 

As always Si, your advice is excellent, and whether it's a true parabola is irrelevant for the average shooter. I spent a lot of hours banging my head against the maths of parabola during my degree.

 

For long range, high AOE gunnery you might need to know the difference from parabolic, but for an airgun the maths is a bit OTT. Let's just say that, for the trajectory to be truly parabolic we would have to ignore the effect of air resistance.

 

I'm a bit of a maths geek, so if anyone is interested here's why it's not a parabola. I totally agree that it's near enough for most shooters, and the following is only of academic interest.

 

Ignoring air resistance would mean that a bullet leaving the barrel with a velocity of 800 fps horizontal velocity would strike the target, at whatever range, with a horizontal velocity of 800 fps. This would mean that the overall velocity of the pellet would increase, and so the pellet/bullet would strike the target with more energy than it started off with. It sounds impossible, until you realise that it would be transferring potential energy due to elevation into kinetic energy.

 

Of course, we know this is not the case. Bullets/pellets slow down as the distance from the muzzle increases, due to deceleration due to air resistance. Now the acceleration due to air resistance varies as a function of the velocity, so unlike gravity it is not a constant, and so the rate of acceleration (negative acceleration it may be, but acceleration it is) changes and the curve is no longer parabolic.

Edited by matt_hooks
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Good vid!

 

One thing thats always confused me is shooting up at a steep angle from the ground, for example alot of my shooting is at crows/pigeon that land in tall trees whislt i sit in cover at the base. I have to aim well below above the cross hair. It kind of makes sense why you have to do this, but when i try to think about it more it confuses me haha

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