Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: whip crack explanation?



on 4/4/2001 12:21 PM, Hugh Haskell at hhaskell@MINDSPRING.COM wrote:

But how is it possible to measure the speed of such a small
object moving such a short distance in a fraction of a
second?
I doubt that it can be done with inexpensive phototimers or
by ordinary movie cameras.


No, not by ordinary cameras.
I had a parent who was into high speed photography,
He had and brought in (and did the photographing) with
the equipment. I only did it the one time as the family
moved, but it did work.

Tim

I can confirm Tim's result (indirectly). My colleague, Loren Winters,
teaches high speed photography fairly routinely, and a couple of
years ago he had some students who were interested in this problem
with regard to snapping towels. The rigged up a high speed video
system and were able to measure the speed of the tip of a snapping
wet towel and found it to be a bit above the local speed of
sound--something like 380-400 m/s.

Years ago, when I was in flight training, we trained for a while in
the old WWII trainer the navy called SNJ (Air Force/Army designation
was AT-6). The engine had a characteristic snapping sound at high
RPM, such as when you take off, which was attributed to the propeller
tips exceeding the speed of sound at these RPM's. A quick calculation
confirmed that when the engine speed was over about 2300 RPM the
propeller tips were travelling at about 400 m/s, enough to create the
snapping sound of a whip as each blade passed. I don't recall the
propeller gear ratio or the blade length now, so I cannot reproduce
the calculation.

Hugh
--

Hugh Haskell
<mailto://haskell@ncssm.edu>
<mailto://hhaskell@mindspring.com>

(919) 467-7610

Let's face it. People use a Mac because they want to, Windows because they
have to..
******************************************************


By current research it seems an immutable fact that the global climate has
warmed... This is evidenced by an increase in lightning storms (Soccorro
Tech in New Mexico has directly related lightning flashes around the globe
via background low-frequency radio waves with an increase in temperature),
and an over-abundance of tropical storms. El Nino used to carry out a
12-year cycle, according to early meteorological studies from the turn of
the century. Now, El Nino cycles have waned to a 4 to 5 year cycle, and the
cycle seems to wane ever more. Given that tropical storms are powered by
evaporation of waters near the equator, it has been intimated that this is
evidence of Global Warming.

Nevertheless, ice core samples support evidence that Ice Ages occur every
30,000 to 50,000 years; the last Ice Age ended about 13,000 years ago.
Ergo, it has been argued that the Global Warming trend is really just an
effect of the world "coming out of" an Ice Age. Therefore it is only
natural that the Earth should warm. We should expect a "flowering" of
non-flowering, non-seasonal plants adapted to warmer climes like ferns, etc.

The real question is, then, if the Earth is warming at an aberrant rate.
Unfortunately, rate of warming is difficult to extract from Ice-core samples
and the like, and given that the last ice age was such a short time ago,
paleobotany hasn't led to many clues, either.

We know that some of our polluting emissions cause greenhouse effects.
Still, with more warming, there will be more evaporation. And with more
evaporation, there should be more condensation, causing more cloud cover and
an occlusion of the Sun, which SHOULD set up a self-regulating system to
maintain balance by causing Global Cooling (James Lovelock, 1972, "Gaia
Hypothesis")

From this I conclude, the Jury is still out; Pauli would be proud, if he had
lived long enough... It would seem, once again, by measuring the system, we
alter the conditions, thus changing the experiment. But we scientists love
to experiment, do we not? Eventually, though, Mother Nature will have the
final word.

nate.
--
Nathaniel Wayne Davis
Physics Teacher
Mountain View High School
haphaestus@earthlink.net