G'day

A while back, someone posted a rather dramatic and painful looking photo of a broken takedown bow that got that way from being dry fired.

Can someone out there please explain to me, the mechanics behind this?  I know you are not supposed to dry fire but what I don't understand is what exactly is going on when you do. And how is an arrow, which really weighs nothing in the grand scheme of things, able to absorb all of that energy when it offers so little resistance to the released string?  

Bit of a physics question but I am confident that many of you are up to the task.

cheers,

Robert

in essence you have answered your own question. the energy stored in the drawn limbs has to go somewhere and without the arrow it's all absorbed by the bow. arrows are light in the grand scheme but they do absorb a lot of energy, hence the archers paradox when the arrow leaves the bow. the heavier the arrow the more energy it takes to propel it and the less energy the bow has left to do something with.

i have had a few accidental dry fires, one last week when a nock was cracked and split off at the release. the arrow dropped straight down and the bow sounded like a shotgun going off. after a thorough inspection the bow seems to have escaped any damage. i was lucky!  

hopefully someone else with a little more knowledge on this can chime in and give you a better understanding.

In most bows 80+% of the stored energy is release on the arrow.  Some approach 90%.  So when you dry fire that is one heck of a lot of energy that has to go somewhere and it us usually not a good place.

Mike

If you have any copies around, look at a bow review in TBM.  The stored energy needs to go somewhere, and that is usually the arrow (0 to 160 fps in 0.0000001 sec), and some noise/heat (friction).  Noise is vibration.  Take two of those away due to no arrow, and it is all vibration.  You just made an earthquake.... and that released energy is going to be released in a continuing forward movement of your limbs as nothing is holding them back.  BOOM! Things are going to break.

From Physics:  A body at rest remains at rest, and a body in motion remains in motion, continuing in a straight line, unless acted upon by equal and opposite forces.  

Gosh, I knew I would use this some day....

BobW

I've been wondering about this as well, thanks for the info....