Re: A Parents' Day gem

[Robert Mathieson <rmathieson@culver.edu>]

It is fascinating to watch a thread evolve. My low velocity pellet shot over
a pond  became a high velocity bullet.  Communication by email has a very
different dynamic than face-to-face conversation. 

Hugh Haskell wrote that   >It sounds like this was a rather informal
"experiment.">

Yes, "quite".  The goal of the day was to shoot at tin cans;  that went
quite well.  I don't remember how the topic came up but my friend speculated
that if we were using high velocity rifles instead of low velocity pump-up
pellet rifles, the bullet (pellet) would stay in the air "lots" longer.  I
said I didn't think it would be "lots" longer and suggested that  a shot
pellet wouldn't stay in the air several times longer than a dropped pellet.
My friend felt that the shot pellet would hit the water much later than the
dropped pellet.  I asked what he meant by  "lots";  after a moments thought
he said "several".  We agreed that several meant more than two.  
 
> So not only was the leveling of the gun barrel only approximate, but how
did you insure that the drop and shoot times were about the same   >

Used one hand to pull the trigger and the other to drop;  I've never checked
the time delay between my hands although my arms appear approximately equal
in length.

> and how did you determine that the landing times were about the same? The
two events had to have been far
> enough apart that sound was not a reliable indicator. Unless both landing
points were in the simultaneous view of at >least one observer (that is to
say, approximately colinear as seen by that observer), and the splashes (I
assume the >shot was fired over water so the dropping bullet would land in
the water and splash like the fired one) were both large >enough to see,
itseems to be quite difficult to establish the simultaneity visually.

One pump in my pump-up pellet rifle gives a velocity of about 100 ft/sec.
Shot from about a meter above the water the flight time is about half a
second.  It's easy to see it hit--50 (or so) feet isn't all that far.  It
did indeed occur to us to use the far edge of the water as a reference and
"aim" at a spot about a meter above that.  Of course, we couldn't use the
sights because the line established by the sights isn't parallel to the
pellet's initial velocity so we tried peering along the barrel.  One shot
and dropped and the other hunkered down.  (I don't know whether or not the
hunkerer thought of colinear;  I think he just tried to see both splashes). 

Did we establish simultaneity (used in the way I think it is being used in
this thread, that delta t is zero)?  Of course not.  Did we establish that
the flight time of the shot pellet was not several times greater than that
of the dropped pellet?  Absolutely.  Close(less than half a second apart)?
Yes.  Not that much different that the standard demonstration using some
sort of launcher/dropper where we all listen for the balls landing (I wonder
if my ears are worse than or better than my eyes at that sort of thing?)

> And it is wrong to secretly skew the experiment so that it appears to come
out "right" even when it hasn't.

Agreed.  I reread what I wrote to see if I had left the impression of
purposeful deception.  I had thought that using the  word "unconciously"
about an aiming bias  would communicate lack of intent rather than concious
ethically wrong behaviour on my part.  I obviously didn't write clearly.

I am interested in learning the difference in flight times for high speed
projectiles-1%, 50%?  Maybe someone will have some quantitative data.

Cheers,

Robert Mathieson
Culver-Stockton College
Canton, MO 63435
(217)231-6000
rmathieson@culver.edu