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Old 3rd October 2013, 09:19 PM
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Brian.Samson Brian.Samson is offline
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Join Date: Jun 2009
Member of: Pontefract, Doncaster Airgun Range
Location: Doncaster
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Originally Posted by rich View Post
I'd like to come back to the sticks in the water analogy. The argument put forward was that the sticks are floating in the flowing water and therefore there is no force upon them by the flow of water.

That will be true, once the sticks have accelerated from zero in the direction of water travel, up to the water speed. Force = mass x acceleration. If the sticks accelerate up to the water speed (and they do) there HAS to be a force acting on them, in that direction.

Now, our little airgun pellet is like the stick. Ultimately, if gravity didn't pull it to the ground first, it would travel along in the wind, at the same speed as the air molecules. Much like a dandelion seed. But initially, at the instant the pellet exits the barrel, it has zero speed in the direction of the wind. Take a broadside wind for example as it's easier to imagine. So, if the pellet accelerates sideways from a zero vector to equilibrium with the wind, there has to be a force acting upon it, same as the stick in the water.

Righto.. I've done a bit of reading up on this now and I'm pretty sure I understand the theory on it. (it's more than just a theory though, and it's not 'my' theory - this is accepted ballistics fact and has been for hundreds of years)

So, the mistake you've made in your statement is this..

When the pellet leaves the barrel, it doesn't accelerate to the speed of the wind, it's instantly inserted into a bunch of molecules that are travelling sideways at say 5mph (in the case of a 5mph 90 degree crosswind) relative to the ground.

So it doesn't accelerate to 5mph, it's not moving sideways at all (relative to the air molecules). Relative to the ground it is moving sideways, but not relative to the air which it is now a part of.

Now how this relates to the theory behind this thread is - if a pellet spends less time in the wind it will without any shadow of a doubt take less wind. So, in theory the pellet with the highest velocity when it reaches the target is likely to be the one that spends less time in the wind. I say likely, because it relies on how accurate you think the trajectory calculation is (and I think it's pretty accurate).
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