75ZT Community

I think I must be going mad.
Keep on thinking of problems that puzzle me. Not relating to my R75 I hasten to add, that's trouble free so far (three years and counting), more to do with the world around us and the anomalies in it.

For instance, we all know that you can't compress a liquid. That's why hydraulic brakes work. On the news tonight there was that chap who had been to the deepest place in the oceans in a submarine, 7 miles down, where the pressure is 16000psi!

So, question: If the water 7 miles down is not compressed, is it more dense? Does it weigh more than surface water? Is it thicker (viscosity) i.e. more difficult to move through?
I worry if I'm not worrying.

Oh dear, I knew that would happen - I've knocked the bottle over - how am I going to to get that stain out by the time she comes back?

See, there's another thing to worry about. I've just read that back after loading it and it says 'related to police getting water cannon'. No it's not. I'll have to get another bottle now.

Talking of oceans and thick water, do we believe that the city of Atlantis ever existed (meant to be 3 miles down)......

Said on the news tonight that the pressure down there was eqivalent to having three double decker buses on your thumb, and don't ask me how they worked it out

It's to do with the total weight of the water above you. If you imagine a postage stamp on the ocean floor. Now imagine a column of water, the same length and width of the stamp extending all the way up to the surface of the water. Now if you could weigh that water you'll find it's a lot! Hence the derived calculation that the force exerted on you at the bottom of the ocean is proportional to how deep you are.

What'll get you is the atmosphere works the same but in reverse - i.e. the pressure at the earths surface is greatest whilst the higher you go, the less it gets (because there is less of it above you).

Yeah right, tis moonshine innit.. Everyone knows you cant get three double decker buses on your thumb!
...

SpongeBob wrote:It's to do with the total weight of the water above you. If you imagine a postage stamp on the ocean floor. Now imagine a column of water, the same length and width of the stamp extending all the way up to the surface of the water. Now if you could weigh that water you'll find it's a lot! Hence the derived calculation that the force exerted on you at the bottom of the ocean is proportional to how deep you are.

What'll get you is the atmosphere works the same but in reverse - i.e. the pressure at the earths surface is greatest whilst the higher you go, the less it gets (because there is less of it above you).

That's only so you can boil a kettle at the top of Everest at 70 degC. I can see it now, 2/6/53, Mallory and Tensing breaking out the primus on that folding-over snow shelf, striking one Swan Vesta after another and being blown out by the gales, saying 'Come on you fool, I've been wondering for years if this will work'.

I don't believe it is more dense because of the pressure, however if it's colder or warmer it will change the density. Water is most dense at around 4 degrees if I remember right, and gets less dense the warmer or colder you go from there.

Jumper wrote:That's only so you can boil a kettle at the top of Everest at 70 degC. I can see it now, 2/6/53, Mallory and Tensing breaking out the primus on that folding-over snow shelf, striking one Swan Vesta after another and being blown out by the gales, saying 'Come on you fool, I've been wondering for years if this will work'.

and then that Yorkshire Tea van pulls up...

Then there's a knock at the tent flap.
"Ellooaahh! Can a int'rest yer in sum good onest broooaaarrrdband from Yorksheerr?"

Duncan wrote:I don't believe it is more dense because of the pressure, however if it's colder or warmer it will change the density. Water is most dense at around 4 degrees if I remember right, and gets less dense the warmer or colder you go from there.

I think you're right. It's at 4 degrees that ice crystals start to form in water (there is a 'Maximum Ice Formation Zone' - ask any butcher) and, as ice has more volume than water (it floats after all) it expands. Something that puzzles me though. Usually, tepmerature increases with pressure. So if the pressure down there is 16000psi, how come the temperature is approaching Absolute Zero? Isn't there a Physics teacher on here?

Jumper wrote:

Duncan wrote:I don't believe it is more dense because of the pressure, however if it's colder or warmer it will change the density. Water is most dense at around 4 degrees if I remember right, and gets less dense the warmer or colder you go from there.

I think you're right. It's at 4 degrees that ice crystals start to form in water (there is a 'Maximum Ice Formation Zone' - ask any butcher) and, as ice has more volume than water (it floats after all) it expands. Something that puzzles me though. Usually, tepmerature increases with pressure. So if the pressure down there is 16000psi, how come the temperature is approaching Absolute Zero? Isn't there a Physics teacher on here?

Yes pressure does normally result in a temperature increase but only on the scale of magnitudes larger than what the oceans can provide

With regards to the oceans, it's simply colder down there because of the lack of sunlight that reaches those parts. The only warming is from thermal vents. Incidentally - as the pressure increases the water cannot form ice crystals as readily so it doesn't actually freeze down there despite being rather chilly. And for the followers of absolute zero, we have this from Wikipedia:-

Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means. A system at absolute zero still possesses quantum mechanical zero-point energy, the energy of its ground state. The kinetic energy of the ground state cannot be removed. However, in the classical interpretation it is zero and the thermal energy of matter vanishes.

The zero point of any thermodynamic temperature scale, such as Kelvin or Rankine, is set at absolute zero. By international agreement, absolute zero is defined as 0K on the Kelvin scale and as −273.15° on the Celsius scale. This equates to −459.67° on the Fahrenheit scale and 0 R on the Rankine scale. Scientists have achieved temperatures very close to absolute zero, where matter exhibits quantum effects such as superconductivity and superfluidity.

SpongeBob wrote:It's to do with the total weight of the water above you. If you imagine a postage stamp on the ocean floor. Now imagine a column of water, the same length and width of the stamp extending all the way up to the surface of the water. Now if you could weigh that water you'll find it's a lot! Hence the derived calculation that the force exerted on you at the bottom of the ocean is proportional to how deep you are.

What'll get you is the atmosphere works the same but in reverse - i.e. the pressure at the earths surface is greatest whilst the higher you go, the less it gets (because there is less of it above you).

Who in their right mind is going to try that experiment when the cost of a 1st class stamp is being hiked to 60p at the end of April????????????????????

...don't the rules of physics work in reverse below sea level?

Also, those who could imagine 3 double deckers on your thumb (or a 3 mile column of water on a postage stamp)probably know a fair bit about hydroponics...

Wouldn't your thumb become really wide therefore spreading the load and reducing the effective pressure to approx 2.75 double decker buses?

Just saying..

Is that a double decker with all the passengers cos all the passengers could be very thin in which case it would be lighter than all the passengers being fat, but there again fat floats

geesmith wrote:
Also, those who could imagine 3 double deckers on your thumb (or a 3 mile column of water on a postage stamp)probably know a fair bit about hydroponics...

Growing plants in water may not have a lot to do with it tho'

Not too sure about my thumb, but once had five double deckers in my fist. Unwrapped, of course.

I was once told that if you could pile enough 10pence pieces on top of one another then there would come a point that the one at the bottom would melt due to the weight of the others on top of it. Presumably, if I did this underwater I would need even more 10 pence pieces 'cause the water would act as a coolant and the coin at the bottom wouldn't get so hot as quick and wouldn't melt as easily. . .

I was also once told that every 3 million years or so, you should remove the glass in your windows and turn it through 180 degrees and then refit it. This is because glass never totally hardens (even tempered glass apparently)so as the glass is ever so slightly 'fluid' it will slowly sink groundwards and you will end up with window panes that are thicker at the bottom than they are at the top.

Me? I'll believe anything.

Don't want to let off a stink bomb at the party, but, this is an old chestnut that I might just be able to pop. There's not many things I know something about so I just can't resist!

Glass. Made from sand, silica, potash, metallic oxides (for colour). All these are stable compounds, in their natural state (at least on this planet). Mixed and melted at upwards of 2000+deg. to turn into its liquid state so it can be formed, worked, shaped. Then allowed to solidify into its combined solid natural state. If left in any position for 10 million years it will probably remain un-bent and unchanged (subject to surface degradation due to atmospheric acidic/alkaline attack).
The Myth. Due to the mists of time (glass has been used and worked for thousands of years in one form or another) it is really unknown how this myth came about, but is generally attributed to lay people observing that glass used in early windows was thicker at the bottom than the top and the assumption that it had flowed downhill was born (mind you, I suspect it may have been a workshop wind-up). In fact it is to do with how the glass is formed. Before float beds were invented for flat glass, all glass was 'blown', or cast, in cylindrical form, cut with shears along its length, and reheated to re-melt it flat. The result was a sheet of glass that was of differing thicknesses across its width. Tons of Georgian and Victorian glass was made this way and can be seen everywhere, but the myth persists. The pieces of glass for windows were placed in their frames thick end down for strength in seating. I have the remains of a Victorian summer house with all of the glass panes exactly like this.

So, if your MGR75 has the base of the screen rather thicker than the top, that doesn't mean it's flowed downhill.

I did say I believe anything - I'll even believe you

(Edited because 'i' before 'e', except after 'c' . . . . . . doh!)