Kinetic Energy / Momentum and traditional archery gear...

[WildmanSC]

Jeff,

No matter which one a person thinks they are banking on, they are in fact banking everything on momentum, truth be known.  I would rather have my longbow or recurve shooting a 10 to 12 gr/pdf arrow in the 170-175 fps range than an 8 gr/pdf arrow in the vicinity of 200-205 fps.  Plus, I don't want my bow absorbing all of the KE, or in your terms PE, I don't get transferred to a light arrow!

Bill

[xia_emperor]

LOL! and away we go.  

[Cupcake]

OK, I can't restrain myself...

K.E. of a bow is 1/2 times mass times velocity squared.

Momentum is mass times velocity.

I looked up some test data taken by Pete Ward on a Cari-bow Perigrine and did a few calculations.

A 452 grain arrow went 187fps
A 702 grain arrow went 156fps

The K.E. is:
452 grain 1128 ft.lb./sec.sec.
702 grain 1220 ft.lb./sec.sec.
A difference of 7.5%

The Momentum is:
452 grain 12.07 ft.lb./sec.
702 grain 15.64 ft.lb./sec.
A difference of 22.8%

Same bow, heavier arrow has quite a bit more momentum and a little more K.E.

An interesting observation in this is that one would conclude that the K.E. should be the same for the two different arrow weights, but it is not.  The heavier arrow has more K.E.

I think it may be that the heavier arrow is accelerated slower, but for a longer time, so it goes faster.  Much like a dragster running a slower time often has a higher terminal speed.

Ain't physics cool?

Enjoy your popcorn folks.  :D  

Kevin out

[Larry247]

[WildmanSC]

Originally posted by Cupcake:

Same bow, heavier arrow has quite a bit more momentum and a little more K.E.

An interesting observation in this is that one would conclude that the K.E. should be the same for the two different arrow weights, but it is not.  The heavier arrow has more K.E.

I think it may be that the heavier arrow is accelerated slower, but for a longer time, so it goes faster.  Much like a dragster running a slower time often has a higher terminal speed.

Kevin out

Kevin,

Actually, the heavier arrow holds its velocity for a longer period of time because it has more MO-mentum!    :D

Bill

[Jeff Strubberg]

I guess my post wasn't very clear.  

I will take momentum of KE because KE is a measure of poetential energy that can be expended in many ways...noise, vibration, etc.  Momentum only measures the energy stored and expended in a single direction.  Energy expended in oscillation and noise are irrelevant.

[Crooked Stic]

Solution-Get a bow that shoots a real heavy arrow real fast!  

[Jason R. Wesbrock]