"David R Brooks" <davebXXX@iinet.net.au> wrote in message
news:43ce15a6$0$23587$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
> Is a supersonic shockwave the explanation of the effect one sometimes
> notices with a nearby lightning strike: see the flash, & hear almost
> simultaneously a sharp crack, like a stick snapping. A second or so
> later, comes the boom. So that crack must have been supersonic?
I doubt it, although undoubtedly there is some amount of supersonic effect
considering the rapid heating pulse. More likely the low frequencies are
bouncing off trees, houses, clouds and whatnot, which also fragment the
sound into a rumble (also attenuating high frequencies).
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
> > but none of the departments listed there seem to qualify as "ID"
> dat komt omdat de ID = Instrumentele Dienst,
> oftewel een ondersteunende dienst,
> die alleen op de "medewerkers" pagina is terug te vinden
Wat dom van mij! Ik was wirksam bij de Technsiche Zaken van be
B-faculteit 1973-79 en af en toe waren wij - verassent zelten - over
iets bezig met julie ...
--
Bill Sloman, Nijmegen
Reply by Everett M. Greene●January 18, 20062006-01-18
"Chuck F. " <cbfalconer@yahoo.com> writes:
> David R Brooks wrote:
> >
> > [snip]
> >>
> > Is a supersonic shockwave the explanation of the effect one
> > sometimes notices with a nearby lightning strike: see the flash,
> > & hear almost simultaneously a sharp crack, like a stick
> > snapping. A second or so later, comes the boom. So that crack
> > must have been supersonic?
>
> Much simpler explanation. The speed of sound varies with frequency.
According to the Flight Test Engineer's Handbook, the speed of
sound varies with temperature. Nothing about frequency in the
equation(s).
Reply by Chuck F.●January 18, 20062006-01-18
grg@umn.edu wrote:
>
> I assumed something in our house wiring was arcing over. Speed
> of light, you know.
What has this got to do with? Include context - most usenet users
cannot conveniently see preceding messages. For how to do it with
the broken google interface, see below. Read the referenced URL.
--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Reply by Stef Mientki●January 18, 20062006-01-18
bill.sloman@ieee.org wrote:
> Stef Mientki wrote:
>
>>bill.sloman@ieee.org wrote:
>>
>>>Stef Mientki wrote:
>>>
>>>
>>>>Ico wrote:
>>>>
>>>>
>>>>>In comp.arch.embedded Stef Mientki <S.Mientki-nospam@mailbox.kun.nl> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>at my work we've a 128 channel 32 (or 34) bit AD converter !!
>>>>>
>>>>>
>>>>>Just curious: what is it used for ?
>>>>>
>>>>
>>>>magnetoencephalography (MEG), functional brain imaging,
>>>>by measuring the magnetic field form active neurons with squids.
>>>
>>>
>>>Working for Peter Hagoort?
>>>
>>
>>No, at the ID
>
>
> "ID" ?
ik dacht dat je bekend was ...
The Donders Centre does have an MEG
dat komt omdat de ID = Instrumentele Dienst,
oftewel een ondersteunende dienst,
die alleen op de "medewerkers" pagina is terug te vinden
cheers,
Stef
>
Reply by ●January 18, 20062006-01-18
I assumed something in our house wiring was arcing over. Speed of
light, you know.
Reply by Paul Keinanen●January 18, 20062006-01-18
On Wed, 18 Jan 2006 09:59:41 -0500, "Chuck F. " <cbfalconer@yahoo.com>
wrote:
>David R Brooks wrote:
>>
>> [snip]
>>>
>> Is a supersonic shockwave the explanation of the effect one
>> sometimes notices with a nearby lightning strike: see the flash,
>> & hear almost simultaneously a sharp crack, like a stick
>> snapping. A second or so later, comes the boom. So that crack
>> must have been supersonic?
>
>Much simpler explanation. The speed of sound varies with frequency.
Or more likely that the audio attenuation is frequency (and
temperature dependant).
If you have a lightning that hits close to you, it might still be 1-2
km long. You will hear the local hit immediately with all high
frequency components present.
However, the sound from the tail of the lightning will arrive 6
seconds later with all high frequency components attenuated and you
will just hear the rumble.
Paul
Reply by Chuck F.●January 18, 20062006-01-18
David R Brooks wrote:
>
> [snip]
>>
> Is a supersonic shockwave the explanation of the effect one
> sometimes notices with a nearby lightning strike: see the flash,
> & hear almost simultaneously a sharp crack, like a stick
> snapping. A second or so later, comes the boom. So that crack
> must have been supersonic?
Much simpler explanation. The speed of sound varies with frequency.
--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Reply by Ken Smith●January 18, 20062006-01-18
In article <pan.2006.01.17.16.56.00.384477@example.net>,
Rich Grise <richgrise@example.net> wrote:
[...]
>It'd be interesting to do an experiment where you sense magnetic fields
>in the body during emotional stimulation - i.e., like watching a good
>movie, or listening to some good music, or picking a fight...
If you are measuring the field in the body, you have to insert the
magnetometer. I don't think we'd hear the music over the "OUCH".
BTW: The heart pumping makes some magnetic noise you'd have to filter
out before you could start looking for other stuff.
--
--
kensmith@rahul.net forging knowledge
Reply by Ken Smith●January 18, 20062006-01-18
In article <43ce15a6$0$23587$5a62ac22@per-qv1-newsreader-01.iinet.net.au>,
David R Brooks <davebXXX@iinet.net.au> wrote:
>Phil Hobbs wrote:
>> Keith wrote:
>[snip]
>>>
>>> Supersonic shock waves. What's next?!
>>>
>>
>> All shock waves are supersonic. That's why it's a shock wave and not an
>> ordinary sound wave. There's a big increase in entropy in its wake, too.
>>
>Is a supersonic shockwave the explanation of the effect one sometimes
>notices with a nearby lightning strike: see the flash, & hear almost
>simultaneously a sharp crack, like a stick snapping. A second or so
>later, comes the boom. So that crack must have been supersonic?
Did the "sharp crack" come out of your radio?
--
--
kensmith@rahul.net forging knowledge