OT but hopefully interesting

Martin.. The speed of sound is 340.29 meters per second so four to five seconds would be about right by the time you see the flash and start counting, we have been lucky so far still no rain.

regards bob

The storm has just arrived here, it went very dark about 20 minutes ago. Started raining with mild thunder and lighting.

Andy M

where's here, I'm Bedford area.

Yes, remember to start "annd one annd two annd three..." though not one annd two annd three..."

Looking at the radar on the met office site there is quite a large and heavy blodge of rain over the north midlands heading NEish. Several weather warnings out, 40 to 50mm of rain possible in 1 to 2 hours...

East Yorkshire, about 3 miles from the northern end of the Humber Bridge.

Regards

Andy M

I should know Andy Dan directed me there, old age I'm afraid :-((

Dave,

What an absolutely fascinating site, have put it in my favourites folder, thanks.

Mart>

I was at a religious convention in Stoke a few weeks back. The final speaker was talking of God's wrath being poured out, and quoting from the book of Revelation. As he was doing so the stadium was struck by lighning, and the most intense thunderstormI have ever experienced echoed around. Now THAT is how a thunderstorm should be experienced. Never seen special effects like it. :)

Alan

...(Martin asked about the time between seeing a lightning flash and hearing the thunder, then estimating the distance between the observer and the storm)

Possibly. The speed of sound varies with the density of the medium through which it is passing. That's why Concorde used to measure its speed using the Mach Ratio.

Yes. If your exact figure above is used, then the time interval would be

5.021511 (recurring) seconds. Much better to say "about four to five seconds per mile..." :-)

Whilst we are talking about bangs & God's Wrath, you might like to look at this site............

Regards,

Kim Siddorn

"MatSav" wrote in message news: snipped-for-privacy@pipex.net...

The local speed of sound is actually *temperature* dependent.

Concorde will have a conventional airspeed indicator and a machmeter, (maybe combined) as do all jet airliners. The main difference being that Concorde can exceed the local speed of sound and have indications in excess of Mach 1 without the wings parting company! The airliner that I fly is limited to Mach 0.8, if you go faster than that then following a triple chime a calm young lady's voice announces ''High Speed'' repeatedly.

Hopefully one day I'll be able to offer advice on engines!

Julian.

Ah but the temperature affects the density of the air, cold air is more dense than hot at the same pressure.

No.

The value of the local speed of sound varies only with temperature. The formula for calculating the local speed of sound (in Kts) is = 38.94 times the square root of the temperature in Kelvin. It's that simple, no density involved.

To clarify:

Mach number is proportional to [Dynamic pressure over density] divided by [Static pressure over density]

density thus cancels out and so Mach # is proportional to Dynamic pressure over Static pressure.

Do you remember the early days when our subsonic jet fighters set speed records, they always did it on a red hot day in the desert, ie the local speed of sound was as high as possible.

Have to go with Dave on this one....it is the density of the air that affects the speed of sound, and also the reason for the choice of weather conditions for high speed record flights. The density is dependant upon the temperature AND pressure. (can never remember whether this is Charles law or Boyles law).

This also holds true for other meduims which is why sound is faster in water, and even faster when passing through many solids.

Speed of sound is related to density. Density is dependant on other factors.

Have a look here, maybe it'll convince you:

My previous explanation was simplified, but more or less lifted straight from one of my old text books. (to make sure I got it correct!)

Density is dependant on temp and pressure (as you state) but isn't a factor WRT the local speed of sound, I produced the calculation in my last post to determine LSS, so please feel free to point out its shortcomings, and how you intend to modify the calculation by including air density to produce correct results - with some worked examples please for clarification!

I'm probably due a bollocking for spamming the NG with offtopic stuff, so I'll not drag on here. Either accept the fact that Mach # is temperature related or please do some fact finding of your own via Google or the lending library.

Julian.

Yup, you are quite correct, sorry.

I never realised that sound waves in air are heat/pressure waves before. The Wikpedia article on "Speed of Sound clarifies things and makes for very interesting reading.

I suppose this means we need to know the height of the sorm clouds and the air temperature to adjust the rate at which we count to find out how far away the storm is.

Alan

Since sound travels faster in water than air, should we also account for whether it's raining?

John

I recall that sound is slowed by rain as it is deflected off the curved surface of the falling drops.

Always summut, isn't there? ;o))

Regards,

Kim Siddorn

Diplomacy done, plates spun, fires fought, maidens eaten - well, three out of four ain't bad

That's OK, it's certainly rather counter-intuitive. I would have thought the same as you had it not been for the boffins that provide explanations in the text books, - I needed to pass a stack of exams many years ago!

Julian.