Science question

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Sloppy Does
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Science question

Post by Sloppy Does » Fri Dec 15, 2017 9:42 pm

I'm not smart enough to know but smart enough to ask. With the very short power stroke of the 308 Short would it lose speed faster than say a micro 335. The one I shot was 314fps out the gate but how well would the short power stroke hold up down range say 35 to 40 yards?
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Re: Science question

Post by SEW » Fri Dec 15, 2017 10:03 pm

Once an arrow has left the bow, it’s all up to the arrow and it’s speed at launch. How it got that is irrelevant.

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xcaliber
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Re: Science question

Post by xcaliber » Fri Dec 15, 2017 10:08 pm

The draw length has zero to do with down range impact. It's speed / weight of projectile. There are many formulas for this calculation, but after a lot of research speed really drives the end result. To make this easier to accept, go to Nikon Dead On, or BDC calculator. Or any archery site that utilizes a calculation tool. You'll find that even though you change weight, speed drives the impact variations at differing yardages. This however does not calculate force which is weight driven over speed. To visualize this imagine a bus hitting a brick wall at 30 MPH, and a moped hitting the same wall same speed. Damages are very different.
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Sloppy Does
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Re: Science question

Post by Sloppy Does » Fri Dec 15, 2017 10:11 pm

Are you saying that if two bows shooting 300FPS but one has a longer power stroke it does not have an advantage down range, they are equal when shot with the same arrow?
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Re: Science question

Post by Hi5 » Fri Dec 15, 2017 11:48 pm

How an arrow attains its speed is not relevant to the issue of how quickly it slows down. So, power stroke is irrelevant to how quickly an arrow slows down.
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BrotherRon
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Re: Science question

Post by BrotherRon » Sat Dec 16, 2017 7:58 am

Correct... once an arrow is in flight it's launching platform has nothing to do with speed loss. :wink:
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Re: Science question

Post by Hunt it » Sat Dec 16, 2017 8:21 am

It's the speed and weight of the projectile - has zero to do with launch method.

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Re: Science question

Post by Heavy Waters » Sat Dec 16, 2017 12:35 pm

Force = mass x acceleration. As soon as the arrow leaves the string, no more force is being applied by the string. The only force applied to the arrow at that point is the force of gravity which pulls the arrow down at 9.8 meters per second every second. The length of time that force is applied to the arrow does not matter. If it leaves the string at 300 feet per second it can only slow down from that point on. A bullet only accelerates while it is in the gun barrel.It starts slowing down as soon as it leaves the barrel.

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Re: Science question

Post by SEW » Tue Dec 19, 2017 10:24 pm

Arrows have a parallel with bullets. That is ballistic coefficient. Bullets can have ballistic coefficients that very greatly even if they weigh the same. Long, sleek bullets like an 80g Amax 224 vs an 80g 380 pistol bullet could be shot at the same speed but the 380 bullet would slow quickly and drop significantly downrange. A 5” feather, heavily helical with a large fixed broadhead launched at 350’/sec and another arrow with offset SK200s and a Schwacker broadhead will fly significantly differently. The first will slow quickly and have a poor trajectory whereas the second one will drop much less.
So, there’s a 3rd and very important factor in arrow flight: ballistic coefficient of the arrow.

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Re: Science question

Post by nchunterkw » Tue Dec 19, 2017 11:28 pm

What SEW said. Different arrows of the samw weight can have much different drag. So 2 arrows could weigh the same and be going the same speed, but the one with more drag will slow down quicker. Of course this will be most noticeable at longer distances. You may not see much difference inside 30 yards.

And to answer your original question, as others have, draw length or power stroke has no effect on how quickly an arrow slows after it leaves the bow.
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