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Prairie Dog
09-27-2015, 11:56 PM
I've been thinking about getting into archery and have subsequently been creeping some archery forums. One question that seems to spark discussion is; when does an arrow reach maximum velocity? Some say the moment the arrow leaves the string while others offer that it will continue to accelerate till about 5 or even 10 yards out.

Thoughts?

Foxer
09-28-2015, 12:05 AM
I just don't see how that's possible - an object cannot undergo acceleration even in space without a force being applied to it. Now - i get that the arrow itself can store energy as it's fired, compressing from the force of the bow much like an atlatl, but even then it needs something to push off of in order to use that energy so i can see it 'pushing' off the string as the string comes to a stop, and that might possibly give teh impression of acceleration a very short distance from the string, but 5 - 10 yards out?!? I don't see how it can undergo acceleration for that kind of distance after it's lost it's ability to push on anything. Even if we say airflow may improve as it straightens out there's still SOME air resistance the whole time. Where would the acceleration come from?

Prairie Dog
09-28-2015, 12:21 AM
I'm of the opinion that once the 'driving force' is removed deceleration begins.


Where would the acceleration come from?

If I was smart enough to answer that I wouldn't have to work for the railroad. :)

Foxer
09-28-2015, 12:41 AM
I'll be honest with ya - and no offense to your friends who're saying acceleration continues out to 10 meters, but i would hazard a guess that it's a simple case of the chrony's having a harder time getting the speed right while the arrow is still doing the 'happy dance' after it leaves the bow, and as the arrow settles down the readings become more accurate. We all know chrony's are weird and wonderful bits of tech - i've seen something sort of similar when trying to chrony shotgun rounds with birdshot, it can produce some very very odd results at different ranges depending on what the wad is doing.

Prairie Dog
09-28-2015, 12:45 AM
I'll be honest with ya - and no offense to your friends who're saying acceleration continues out to 10 meters

No offense taken, as I indicated it was from creeping archery forums.

Foxer
09-28-2015, 09:08 AM
No offense taken, as I indicated it was from creeping archery forums.
Well i didn't know - you could have some creepy archer friends on various forums :)

Baddog377
09-28-2015, 09:58 AM
Agreed with others here, once it leaves the string and no further force is applied, then no further acceleration is possible. Even the stored energy of a flexing arrow seems dubious, as an arrow is basically a linear stick, any flex / push would have nothing to push off of and would be countered anyway by an equal and opposite reaction from the front. never mind that it would then flex the other way using up any energy gained.

kennymo
09-28-2015, 10:52 AM
Agreed with others here, once it leaves the string and no further force is applied, then no further acceleration is possible. Even the stored energy of a flexing arrow seems dubious, as an arrow is basically a linear stick, any flex / push would have nothing to push off of and would be countered anyway by an equal and opposite reaction from the front. never mind that it would then flex the other way using up any energy gained.

The flex is side to side as well, the only thing I can see (as mentioned) is bad chrony readings caused by the arrow whipping back and forth. It could give the appearance of the arrow head leaping forward as it straightens, but would basically be an illusion dependant on the exact moment the speed is measured. But speeding up after it leaves the bow should be impossible according to physics.....

Camo tung
09-28-2015, 02:58 PM
I don't feel like doing the calculations on paper, it would be more fun to set up multiple chronys and get some practice in....test the "theory" Mythbusters style!

On the same thought: didn't we discuss something similar with a bullet leaving a barrel? Can't remember if we did or if it was just bacon-induced philosophizing.

Foxer
09-28-2015, 07:45 PM
I don't feel like doing the calculations on paper, it would be more fun to set up multiple chronys and get some practice in....test the "theory" Mythbusters style!

On the same thought: didn't we discuss something similar with a bullet leaving a barrel? Can't remember if we did or if it was just bacon-induced philosophizing.

I don't remember that, but at least it's conceivably possible considering gasses are still escaping behind the bullet so maybe there's something to push it after it leaves the barrel... but with a bow, there's a whole lotta nuthin.

Justice
09-30-2015, 10:56 AM
Bullets don't accelerate after leaving the barrel. Arrows don't accelerate after leaving the string. Like Baddog377 says, no force is being applied to either other than gravity and air resistance.
What you will see with an arrow is the fletching start to work. Very cool thing it is too. Just like a switch being thrown, the arrow stops oscillating and starts to fly true.
"...thinking about getting into archery..." Buy a copy of The Archer's Bible by Fred Bear. $26.85Cdn on Amazon.ca. Covers a lot of stuff.