View previous topic | View next topic

Helium

Page 5 of 8
Goto page Previous  1, 2, 3, 4, 5, 6, 7, 8  Next

PDR
642105.  Mon Nov 30, 2009 5:59 pm Reply with quote

Aircraft tyres (and those of high performance sports cars) are usually filled with dried nitrogen, but this is to prevent problems at very high temperatures under braking when any oxygen inside the tyre could be a fire risk, and any humidity cuases non-linear pressure characteristics.

PDR

 
PDR
642107.  Mon Nov 30, 2009 6:03 pm Reply with quote

Davini994 wrote:


(a discussion on the effects of bouyancy on acceleration due to gravity)



Having thought about this you are quite right, and I was completely wrong (that'll teach me to try to covertly reply to posts in the middle of a mind-numbingly boring Project Status Review). Of course the acceleration will change where the net weight changes but the mass the same!

Apologies to all for the klaxons.

PDR

 
Davini994
642130.  Mon Nov 30, 2009 8:12 pm Reply with quote

Gosh, I'm jolly proud to be right about something. In fact, I've already framed a copy of your post:

 
PDR
642163.  Tue Dec 01, 2009 4:33 am Reply with quote

Davini994 wrote:
Gosh, I'm jolly proud to be right about something.


Is it really that unique an experience?

:0)

PDR

 
Davini994
642215.  Tue Dec 01, 2009 7:35 am Reply with quote

Yes, I'm very left wing usually.

 
PDR
642286.  Tue Dec 01, 2009 12:07 pm Reply with quote

A dominant left wing will result in a marked tendence to turn to the right - as any aeronatutical engineer will confirm.

PDR

 
gruff5
642320.  Tue Dec 01, 2009 1:06 pm Reply with quote

Nice one, PDR! Now, if only politicians could behave like you :-)

 
Davini994
642362.  Tue Dec 01, 2009 4:13 pm Reply with quote

Indeed, very impressive.

The older I get the more left wing I get I think!

 
PDR
642388.  Tue Dec 01, 2009 6:07 pm Reply with quote

gruff5 wrote:
Nice one, PDR! Now, if only politicians could behave like you :-)


It's a spare personality that I'm running in for a friend.

PDR

 
Hydra-Lernae
648226.  Sun Dec 20, 2009 3:05 pm Reply with quote

Quote:
Wiki.Answers.com wrote:
What is the volume of a football field? Answer Can be anywhere from 80 decibals to 130 decibals in a college stadium.

Hmm... how many decibals in a cubic litre... something's not quite right here...

(should that be decibels?)


Erm... Decibels is usually a unit used for sound volume, not space volume, and I think that's what the answer means; i.e. not the space volume, but the sound volume when a game is on. Decilitres would have been correct. But yes, it should have been decibles, with an "e". Cubic litre is also wrong, since a litre (or liter) is already a volume unit, hence "cubic" in itself. I am prepared to be corrected though.

 
Celebaelin
648257.  Sun Dec 20, 2009 4:17 pm Reply with quote

Hydra-Lernae wrote:
But yes, it should have been decibles, with an "e".

Decibels - you were right the first time and btw I suspect I bit of deliberate misunderstanding with comedic intent.

 
PDR
648262.  Sun Dec 20, 2009 4:41 pm Reply with quote

Actually the deciBell is a scale used throughout engineering for any property which has a logarithmic characteristic.

PDR

 
Celebaelin
648276.  Sun Dec 20, 2009 5:13 pm Reply with quote

But the specific scale which refers to volume is the decibel - a whole raft of Google hits come up, number 1 being Wiki unsurprisingly.

http://en.wikipedia.org/wiki/Decibel

Interestingly, and perhaps alarmingly from your perspective, if you search for decibell there are no hits in the top 50 using that spelling.

 
gruff5
648409.  Mon Dec 21, 2009 6:03 am Reply with quote

"Simon Cowell at 0 decibels" should be a top 50 hit.

 
suze
648442.  Mon Dec 21, 2009 7:44 am Reply with quote

You'd still be able to hear him, if your hearing was excellent!

As noted above, the decibel has a large number of uses, much as the layperson is only familiar with it as a measure of "loudness" (properly sound pressure). But I shall confine myself here to that use of the unit

Since it is a relative rather than an absolute unit and is defined logarithmically, defining 0 dB as some hypothetical "utter silence" would make the math rather tricky.

0 dB is theoretically defined as the minimum sound level of a pure tone at 1,000 Hz which an "average human ear" with "undamaged hearing" can hear in the absence of other audible sounds. (There are lengthy formal definitions of the two bits in quotes.)

In fact, experimental research shows that few adults can actually hear the prescribed sound at less than 5 dB. But that changes as the frequency changes - a lot of people can hear a tone at 2,000 Hz at a lower sound level than they can a tone at 1,000 Hz.

It also changes according to the duration of the tone - unsurprisingly, some people fail to hear the tone if it is played for a very short time but hear it if played for longer. (Up to about 0.3 seconds - after that length of time, if you don't hear it, then you won't hear it if it's played for a week.)

And accordingly, there are some people who can hear a sound quieter than the reference for 0 dB. Those people are most often girls under about 12, but not always.

 

Page 5 of 8
Goto page Previous  1, 2, 3, 4, 5, 6, 7, 8  Next

All times are GMT - 5 Hours


Display posts from previous:   

Search Search Forums

Powered by phpBB © 2001, 2002 phpBB Group