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RE: Compound bow - set up question
But the peep sight would have to be at a 45degree angle to the bow sight on full draw and that is not realistic. For my illustration (wheter it's right or wrong....I don't know) what difference does it make......as long as it shows the line of the arrow and the line of the sight line crossing at some point in front of the shooter....and reconnecting at the intended target? I could make the sight line much less of a grade. But.....for the purposes of what I'm looking for....I don't see the point. If you can explain to me why that's important.....I'm all ears. It's not to scale, either. And while it was wriiten about firearms, the principiles are the same as what you are describing here. The arrow, as it leaves the bow, does NOT travel a straight line. It travels in a parabolic curve, whose rate of fall increases as range increases. The arrow starts falling the instant it comes out of the bow, so we must aim the bow upwards (via our sights/line of sight/which IS a straight line) to make this curve that the arrow is traveling intersect with the staight line that our sight follows. Is that what you're depicting? And you can launch an arrow perfectly parallel to surface of the earth, it just depends where your target is. |
RE: Compound bow - set up question
I'd saythe stetch is correct mainly because of the height of the target. Something that has been mentioned.
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RE: Compound bow - set up question
OK.....I'm not disagreeing with you....I just want to know why it's traveling on this curve? And....how does it do this (law?) if we've set up our bow with the arrow level? I'd like to understand this. We set our bow up to ensure that the arrow is perpendicular to the string, the only way to accurately do that is to use bubble levels. Thats it. When we shoot at things far away we have to aim slightly up to conteract gravity. So I think you've got it. We set up level, aim at a target 20 yrds away which makes the arrow at a3 degree angle of relative to level (for illustrative purposes), because we raise the arrow rest up w/ the sight to aim, and the nock stays in the same place. Then we release the arrow travels up and passes through the sight line because when it leaves the bow it has some forces from the bow pushing it up. When gravity overtakes the forces fromthe bow the arrow begins to fall. And we hope it intersects the line of sight at the target. Think of throwing a ball straight up, its going to come down, eventually all the force we put in the ball is overtaken by gravitational forces. |
RE: Compound bow - set up question
Bob...I didn't set out to draw something "incorrect":D. I hope it makes sense.
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RE: Compound bow - set up question
Okay Jeff, most of your last post was spot on. We are saying pretty much the same thing, just in different ways.;)
The reason the arrow does not travel a straight line is because as soon as it leaves the bow, gravity begins to accelerate the arrow towards the earth at 32 fps squared. The farther the arrow falls, the faster it falls... Acceleration due to gravity is not a linear function (it will not plot as a straight line on a graph), it is a squared function, which means it's rate of fall gets faster the further it falls. It will plot as a curve on a graph. If it fell at a steady rate all of your sight pins would be the same distance apart, but we know this is not true. The further the distance the further apart the pins get. This is due to two factors, one, the force of gravity keeps accelerating the arrow towards earth faster and faster, and it is compounded by the fact that the arrow is slowing down horizontally because of airresistance, allowinggravity more time to work on the arrow. You see, this is really a problem ruled by time... Once there is nothing left holding the arrow up in the air,resticting it's fall, the effects of gravity take over. In theory, in a vaccuum, disregarding the curvature of the earth;), you could shoot an arrow perfectly parallel to the earths surface at the exact same instant that you dropped a second arrow, and they would both hit the ground at the same time. This fact really takes folks aback the first time they hear it, but it is true. Both arrows are accelerated towards the earth at the same speed due to gravity, it is acting on both arrows equally. One just travels a much farther horizontal distance before it impacts the earth. The law? I think it had to do with that Newton guy and the apple.:D:D:D Sorry, don't know the number of that law, but I'm sure it's in the top five laws of physics. As far as your picture dipictions, I saw nothing wrong on them that needed to be corrected. Sorry if you took my post that way. |
RE: Compound bow - set up question
Jeff, your sketch is correct. Did it provide any information to you? To me, I see that if you move the target up/down, and/or the bow up/down, the arrow CANNOT be parallel to the ground any more as indicated in your sketch. (I better list my obvious assumption since you seem very interested in picking nits today: you dont move 'each' the same distance one direction)
It is still parallel to the string when you let down (obviously) even if no longer parallel to the ground when you, say, move bow down 2 feet. What questions are you still struggling with? To me, by your sketch, you have a grasp of everything you have 'discussed' |
RE: Compound bow - set up question
ORIGINAL: Critr-Gitr Okay Jeff, most of your last post was spot on. We are saying pretty much the same thing, just in different ways.;) The reason the arrow does not travel a straight line is because as soon as it leaves the bow, gravity begins to accelerate the arrow towards the earth at 32 fps squared. The farther the arrow falls, the faster it falls... Acceleration due to gravity is not a linear function (it will not plot as a straight line on a graph), it is a squared function, which means it's rate of fall gets faster the further it falls. It will plot as a curve on a graph. If it fell at a steady rate all of your sight pins would be the same distance apart, but we know this is not true. The further the distance the further apart the pins get. This is due to two factors, one, the force of gravity keeps accelerating the arrow towards earth faster and faster, and it is compounded by the fact that the arrow is slowing down horizontally because of airresistance, allowinggravity more time to work on the arrow. You see, this is really a problem ruled by time... Once there is nothing left holding the arrow up in the air,resticting it's fall, the effects of gravity take over. In theory, in a vaccuum, disregarding the curvature of the earth;), you could shoot an arrow perfectly parallel to the earths surface at the exact same instant that you dropped a second arrow, and they would both hit the ground at the same time. This fact really takes folks aback the first time they hear it, but it is true. Both arrows are accelerated towards the earth at the same speed due to gravity, it is acting on both arrows equally. One just travels a much farther horizontal distance before it impacts the earth. The law? I think it had to do with that Newton guy and the apple.:D:D:D Sorry, don't know the number of that law, but I'm sure it's in the top five laws of physics. As far as your picture dipictions, I saw nothing wrong on them that needed to be corrected. Sorry if you took my post that way. |
RE: Compound bow - set up question
WOW, way TMI but still a good read.
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RE: Compound bow - set up question
Jeff, your sketch is correct. Did it provide any information to you? To me, I see that if you move the target up/down, and/or the bow up/down, the arrow CANNOT be parallel to the ground any more as indicated in your sketch. (I better list my obvious assumption since you seem very interested in picking nits today: you dont move 'each' the same distance one direction) OK.....so that being what "is"...... What happens on the straight down shot?.....since gravity becomes a non-factor? I may have just proved MYSELF wrong in a previous post......which was what I was after.;) Assuming the shooter/hunter was 20yds up in the tree (for this exercise).......it would seem the lines would NOT meet back at 20yds (even though they WOULD still meet at 'per Matt/PA' 8yds)......and the shooter would shoot HIGH if he utilized his 20yd pin. Is THIS incorrect/correct logic? |
RE: Compound bow - set up question
That absolutely can be done through a shooter machine, not human. The machine would need set up at full draw with the arrow parallel/level to ground and the bow shot. The target then would need to be moved up or down depending on where the drop of the arrow hits the target. Then and only then could you sight in your pin to the target.
:D OR, The target remain stationary and the shooting machine raised or lowered until the arrow impact/drops hits the target and then and only then could the pin be moved into position. :D |
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