# archery

Aodhan Ite an Fhithich aodhan at dobharchu.org
Mon Mar 27 17:15:03 PST 1995

```Dia duit!

[Replying to a message of "Mark Harris"  to All]

Stefan,

"H> Firstly, (1) F = M * a -- that is, force = mass x acceleration (not
"H> velocity).

>>>>>>
"H> Please recheck this. Using this equation if an object hits you at a
"H> constant velocity (ie: a = 0) then it hits with no force. I find it
"H> hard to believe that the non-accelerating piano at a constant 30 MPH
"H> is going  to hit softer than the bottle rocket going from 0 MPH to
"H> whatever. <<<<<

The equation *is* correct, however, your application of it is not.

A free-flying bolt is under going two forms of acceleration:  gravity trying
to pull it to the ground and drag trying to slow it down.  More germane,
however, is the fact that the bolt undergoes a negative acceleration when it
hits something.  The Kinetic Energy of the bolt [KE = M * (V ** 2)] is
transfered to the target (less some loss due to compression of the blunt).
This transfer takes place over some period of time (let's call it Ti - time of
impact).  Thus, the acceration is the change in velocity over the time
required for that change [a = V / Ti] and equation (1) gives you the force of
the impact.

As someone once said, "I don't mind falling, it's that sudden stop at the
end..."

Feicfidh me' ari's thu',

Aodhan
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Baron Aodhan Ite an Fhithich    aodhan at dobharchu.org
Master of the Laurel            Lough na Dobharchu' BBS  1-713-338-2570
mka David H. Brummel            1:106/22  180:11/22  762:2200/2
SCA Member 02245                Barony of Loch Soilleir, Ansteorra
http://www.phoenix.net/~dbrummel
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plummety sable and argent on a sun of eight rays or a feather bendwise
sinister sable
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No bird soars too high, if he soars with his own wings. - Blake
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