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Login Name Post: Shooting up        (Topic#308270)
Elnathan 
50 Cal.
Posts: 1263
09-18-18 06:20 PM - Post#1703162    

    In response to Spence10

  • Spence10 Said:

As I understand it, the idea is that gravity supposedly only works on the horizontal component of the ball's travel, not the slant one, so drop would be less and the gun would therefor shoot high. Someone who sees it that way, is that the idea?

Spence



Hmmm. No, but that is a simplified mathematical model that works well enough to be useful in the field, or at least so I am told. Again, I haven't actually tried it.

Gravity pulls down, i.e., towards the earth, at a constant force. The angle at which it pulls relative to the initial path of the bullet depends on the direction. If the bullet initally is traveling horizontally (the barrel being held exactly horizontally) the force exerted the propellant and the force of gravity are acting independently, one forcing the ball in one direction and one in another - the curve in the result of those two forces (plus wind resistance) acting on a single object. Shoot upward, and the force of the propellant and gravity are now partially cancelling each other out. Here is a diagram that might or might not help:

g=gravity
p=propellant
w=wind resistance



In the upward shot the gravity is now partially pulling against the force of the propellant, and as the angle changes the exact interaction will change. Wind resistance will continue to act on the ball proportionate to its velocity regardless of its path, which is why its vector is drawn as curved curved. Eventually, as the angle rises to straight up and down, the trajectory of the shot will become straight as all three forces now act in direct line with each other. This will obvious alter the distance at which the line of sight and the path of the ball converge - whether this means you should hold high or low depends on the range and where the lines converge on the new trajectory.

Unless you live in Black Hand's world, in which shooting up is easy but standing up may be difficult...


Hopefully that all makes sense. It has been 18 years since I sat in my father's high school physics class and learned about force vectors, and while I think I remember the principles I've pretty much forgotten all the math and the details about how to diagram the vectors. I'm also kind of sleep deprived at the moment...

 
Spence10 
Cannon
Posts: 6978
09-18-18 07:05 PM - Post#1703167    

    In response to Elnathan

  • Elnathan Said:
Hopefully that all makes sense.


Well, not totally.

You seem to be describing the rather standard explanation of why bullets shoot in something similar to a parabola rather than in a straight line. It would be easier for anyone to get their head around if you left the bit about shooting straight up and straight down out of the discussion. The effect of gravity on bullet velocity and thus trajectory is negligible and just tends to add unneeded complexity to an already complex problem.

Mainly, though, what I was asking about was the idea that people put forward that you only need to consider the horizontal distance from shooter to target when shooting uphill or downhill. If you touched on that question I missed it.

BTW, the gravity vector is always perfectly vertical, even Black Hand's, as he was at pains to point out.

Spence




 
Colorado Clyde 
Cannon
Posts: 15075
Colorado Clyde
09-18-18 07:13 PM - Post#1703168    

    In response to Elnathan

Elnathan is right.... Two bullets will only strike the ground at the same time if they are perfectly parallel to each other ....And in a vacuum, as air resistance can provide lift counteracting gravity.
Especially a rotating sphere. like a round ball...
this is known as the Kutta-Joukowski lift theorem.
Lift per unit length of a cylinder acts perpendicular to the velocity.

All that is necessary to create lift is to turn a flow of air. The airfoil of a wing turns a flow, and so does a rotating cylinder. A spinning ball also turns a flow and generates an aerodynamic lift force.

Yes!....It's rocket science....


 
Spence10 
Cannon
Posts: 6978
09-18-18 07:38 PM - Post#1703171    

    In response to Colorado Clyde

Where would you be without Wikipedia, Clyde?

Spence

 
azmntman 
75 Cal.
Posts: 5689
azmntman
09-18-18 08:03 PM - Post#1703173    

    In response to Spence10

so should I shoot hi, low, dead on or just shoot em on the ground only?



 
Elnathan 
50 Cal.
Posts: 1263
09-18-18 08:31 PM - Post#1703176    

    In response to Spence10

  • Spence10 Said:


You seem to be describing the rather standard explanation of why bullets shoot in something similar to a parabola rather than in a straight line. It would be easier for anyone to get their head around if you left the bit about shooting straight up and straight down out of the discussion. The effect of gravity on bullet velocity and thus trajectory is negligible and just tends to add unneeded complexity to an already complex problem.





Why yes, yes I am. The shape of that trajectory will change as the angle changes, though. That is why I keep harping straight up and straight down - the trajectory changes from a parabolic arch to straight line, proof positive that the trajectory does not stay constant and should be really easy to visualize.

Black Hand's suggestion that the trajectory does not alter regardless of the elevation of the bullet is nonsense precisely because the vector of gravity remains vertical. Since it remains vertical while the vector of the propellant/angle of the barrel changes, the relationship between the two vectors changes. Since the relationship between the two vectors changes, the trajectory changes. Simple, really.

  • Quote:
Mainly, though, what I was asking about was the idea that people put forward that you only need to consider the horizontal distance from shooter to target when shooting uphill or downhill. If you touched on that question I missed it.




I did. My guess was "false but useful" - which is to say that your state reason for why it works would probably give a physicist fits but the actual results would close enough to perfect that you wouldn't care.

Edited by Elnathan on 09-18-18 08:46 PM. Reason for edit: No reason given.

 
Colorado Clyde 
Cannon
Posts: 15075
Colorado Clyde
09-18-18 08:58 PM - Post#1703177    

    In response to Spence10

  • Spence10 Said:
Where would you be without Wikipedia, Clyde?

Spence



Actually, I got it from N.A.S.A. but, I was given a set of encyclopedias as a kindergartener...


 
Spence10 
Cannon
Posts: 6978
09-18-18 09:46 PM - Post#1703186    

    In response to Elnathan

  • Elnathan Said:
The shape of that trajectory will change as the angle changes, though.

[clip]

Black Hand's suggestion that the trajectory does not alter regardless of the elevation of the bullet is nonsense precisely because the vector of gravity remains vertical. Since it remains vertical while the vector of the propellant/angle of the barrel changes, the relationship between the two vectors changes. Since the relationship between the two vectors changes, the trajectory changes. Simple, really.


I think you are seriously overestimating the change in trajectory because of the elevated barrel. Any change is negligible.

Simple, maybe, wrong, certainly.

Characterizing an argument in discussions since as this as nonsense is unnecessary and not very friendly.

Spemce





 
azmntman 
75 Cal.
Posts: 5689
azmntman
09-18-18 10:15 PM - Post#1703192    

    In response to Spence10

Ahhh guys lighten up! We all went to different high schools and had different teachers teaching the same thing differently. I of course was out hunting when they taught shooting parallels n triangles n such. I will get me a target and put it on a string and throw over a limb and do a test and then we will now to shoot a tad low, a tad high or right in the eye

All this math stuff I learned a longgg time ago is REALLY simple to learn (and I was VERY good at math back in the day). The rule to really learning it was the TEACHER. They all teach the same thing but some of em cannot get through period. In Chemistry we had a teacher that reached exactly one student (a hippie pot head Italian kid that was pretty cool). The rest of us graduated having NO CLUE



 
Skychief 
69 Cal.
Posts: 3505
Skychief
09-18-18 10:16 PM - Post#1703193    

    In response to Spence10

To all, I brought a big old boar fox squirrel (the type destined for the slow cooker) out of a beech tree this evening. The shot was angled upward of course (approximately 20 degrees short of vertical) and his vector, soon after, became straight down vertical (he would have done Sir Isaak Newton proud). Point of aim was right at his beak, about 25-30 yards from my muzzle. No problem-o.

Lord love a smoothbore!

Good hunting all, Skychief

 
Colorado Clyde 
Cannon
Posts: 15075
Colorado Clyde
09-18-18 10:40 PM - Post#1703198    

    In response to Skychief

Smoothbores can defy physics....

Why I shot one at a target and it put a hundred holes in it, yet I only fired once.......

I shot a bird with a smoothbore once and the bird completely disappeared.....All that was left was a couple feathers..... I think the gun opened up a worm hole or something that the bird flew into......That's some quantum level stuff right there....

Yep!....Smoothbores, they can defy physics....


 
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