Well lets just say a pint of water that's just reached boiling point but no heat is being applied but is still very hot v a pint of cold water straight from your tap.

At what pressure is it boiling - atmospheric (sea level), vacuum or what?

 

You don't get pure water out of your tap. Are we assuming that both samples are pure water?What are you using to freeze the samples. Are you talking about dropping both samples into identical freezers at -32C and seeing which is the first to become solid.

Edited July 19, 20196 yr by vfr400

This water freezing thing was something I read years ago, it didn't mention any variables just two masses of water one cold and one very hot, which would freeze first.

I suppose you could say two empty containers, fill one with water from a tap the other water from a kettle that's just come to the boil. Subject them to a below zero temperature at atmospheric pressure...which solidifies fastest, the hot container or the cold ? I could also add 'and why ?'

Like everything, external conditions affect how things behave. You also have to be careful about I itial conditions, like what constitutes a pint of boiling water. Say you took two 1 pint beakers of water and boiled one of them. When it's boiling, it'll have a lot less water in it because some will be displaced by the bubbles and the rest will expand to a lower density and some will overflow the rim.

If I can remember my physics lessons correctly in your instance vfr the density wouldn't change because the water was boiling. It's like hard water v soft, hard is very slightly heavier but the density is the same hard or soft.

 

Back to the which freezes first though, boiling or cold. I suppose most people would say the cold water because it's already part way there, others might say the boiling because it can't be that easy.

 

The answer is boiling water freezes faster than cold, the reason being some mass would be lost through steam vapour so there's less to freeze.

 

So now how come a glass of cloudy hard water is no denser than a glass of perfectly clear soft water ?

If I can remember my physics lessons correctly in your instance vfr the density wouldn't change because the water was boiling. It's like hard water v soft, hard is very slightly heavier but the density is the same hard or soft.

 

Back to the which freezes first though, boiling or cold. I suppose most people would say the cold water because it's already part way there, others might say the boiling because it can't be that easy.

 

The answer is boiling water freezes faster than cold, the reason being some mass would be lost through steam vapour so there's less to freeze.

 

So now how come a glass of cloudy hard water is no denser than a glass of perfectly clear soft water ?

You're right but there's a lot more to it than that, it's one of those phenomena that are contrary to initial instincts. Here's a good explanation:

https://en.wikipedia.org/wiki/Mpemba_effect

Fascinating read that, thanks for posting. I've always seen it as hot water freezing quicker because of evaporation but as you rightly there's a lot more to it than that. Interestingly even now no one really has a definitive answer.

 

Finally.....when I was a kid many moons ago I use to help out delivering milk for a local dairy, 12 years old and working hard, no EU rules in those days.

I can still remember sitting in an old milk delivery lorry waiting for the dairyman to emerge from a club having dropped off some milk and downed a few free pints while he was at it (sign of the times).

It was raining at the time and I observed rainwater running up, yes up telephone wires not down as you would expect. There's a reason for this phenomena but I can't recall offhand what it is.

I'll search later unless some one beats me to it.

Funny you should mention this, been looking at getting one for while but just never got around to it. All sorted now, just ordered it thanks! At £14 if it turns out to be rubbish it's not the end of the world!

I hate to be the bearer of bad news but I had one of these which I could hear working as the bike thief rode off after cutting a cable lock. Presumably he gave it a good kicking when he got out of sight. Which is what I would have given him if I had been able to run faster. Perhaps I should lay of the cakes and biscuits as suggested elsewhere.

I hate to be the bearer of bad news but I had one of these which I could hear working as the bike thief rode off after cutting a cable lock. Presumably he gave it a good kicking when he got out of sight. Which is what I would have given him if I had been able to run faster. Perhaps I should lay of the cakes and biscuits as suggested elsewhere.

 

I don't expect a lot for £14, my bike is never far from me and I can run so it may just help!

If I can remember my physics lessons correctly in your instance vfr the density wouldn't change because the water was boiling. It's like hard water v soft, hard is very slightly heavier but the density is the same hard or soft.

 

Back to the which freezes first though, boiling or cold. I suppose most people would say the cold water because it's already part way there, others might say the boiling because it can't be that easy.

 

The answer is boiling water freezes faster than cold, the reason being some mass would be lost through steam vapour so there's less to freeze.

 

So now how come a glass of cloudy hard water is no denser than a glass of perfectly clear soft water ?

That's not right. It takes time for the evaporation to bring the temperature down to the same as the cold water. After that, they're equal. The amount of mass lost by the steam would be insignificant. Try it. Put a mug of boiling water on your kitchen scales and see the difference in weight from initial to cold. You won't even see a gram of difference unless you put a fan on it. The only way the hot water can beat the cold water is by getting better heat transfer. The only way that could happen, assuming all conditions are equal would be if a convection current started, like you have in the oceans. That's feasible as long as you have the right shaped vessel, otherwise the cold will always beat the hot.

That's not right. It takes time for the evaporation to bring the temperature down to the same as the cold water. After that, they're equal. The amount of mass lost by the steam would be insignificant. Try it. Put a mug of boiling water on your kitchen scales and see the difference in weight from initial to cold. You won't even see a gram of difference unless you put a fan on it. The only way the hot water can beat the cold water is by getting better heat transfer. The only way that could happen, assuming all conditions are equal would be if a convection current started, like you have in the oceans. That's feasible as long as you have the right shaped vessel, otherwise the cold will always beat the hot.

That's not what the experiments show, this is the best explanation I could find:

https://en.wikipedia.org/wiki/Mpemba_effect

That's not what the experiments show, this is the best explanation I could find:

https://en.wikipedia.org/wiki/Mpemba_effect

Did you read this bit?

"There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner "

 

There exists a set of parameters where it can happen doesn't mean that it will happen when you try it. Basically, there is one set of parameters where it can happen and thousands of sets where it won't.

 

Later in that article:

"In 2016, Burridge and Linden defined the criterion as the time to reach 0 °C (32 °F), carried out experiments and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers. They say, "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect".

"There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner "

 

water freezes around seed crystals - like Champagne bubbles.

If you have very clean water, with little dissolved salts (eg carbonates and oxides of magnesium, calcium, iron etc), then at below a certain concentration, the movement of those seeds become much more important, causing the previously hot water container (in which the seeds move faster and are better dispersed) to freeze at normal temperature (which is zero Celsius at 1 atm) while the colder water will go supercooled without freezing.

BTW, you cannot derive 'free energy' from this.

Edited July 22, 20196 yr by Woosh

water freezes around seed crystals - like Champagne bubbles.

If you have very clean water, with little dissolved salts (eg carbonates and oxides of magnesium, calcium, iron etc), then at below a certain concentration, the movement of those seeds become much more important, causing the previously hot water container (in which the seeds move faster and are better dispersed) to freeze at normal temperature (which is zero Celsius at 1 atm) while the colder water will go supercooled without freezing.

BTW, you cannot derive 'free energy' from this.

Can you get free water by planting the seeds? I'll look out for them at the garden centre next time I go there for my virgin boy eggs.

Did you read this bit?

"There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner "

 

There exists a set of parameters where it can happen doesn't mean that it will happen when you try it. Basically, there is one set of parameters where it can happen and thousands of sets where it won't.

 

Yes, it's rather badly worded isn't it. The effect has been widely observed since the days Aristotle, so there are clearly many sets of initial parameters where the effect is observed, many "thousands" even.

Later in that article:

"In 2016, Burridge and Linden defined the criterion as the time to reach 0 °C (32 °F), carried out experiments and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers. They say, "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect".

 

So their results invalidate the research of many others eh? That's not quite how scientific method works, try Googling "Mpemba effect" there are lots of write-ups about it.

Can you get free water by planting the seeds?

the idea of using seeds is not far fetched.

The Star Wars 'vaporator' may be one of those water collector working on this sort of idea.

Air containing a little humidity is cooled, releasing water. You need seeds, around them the water droplets form.

https://cdn.cnn.com/cnnnext/dam/assets/170420124634-star-wars-vaporator-exlarge-169.jpg

You can of course see the clouds and create rain, I think they use iodine crystals.

That should read 'seed', I believe the Russians do it a lot.

Yes, it's rather badly worded isn't it. The effect has been widely observed since the days Aristotle, so there are clearly many sets of initial parameters where the effect is observed, many "thousands" even.

 

 

 

So their results invalidate the research of many others eh? That's not quite how scientific method works, try Googling "Mpemba effect" there are lots of write-ups about it.

No, it doesn't invalidate any research. The effect is real, but it seems that nobody can agree what it is and how it happens. The problem is that it's not repeatable because the initial conditions that create it are difficult to pin down. You can't say that it's a rule that hot water freezes before cold water. The likelihood is that it won't, but in some circumstances, it apparently can, though they don't seem to have pinned down exactly what that means. The latest research showed that the hot water doesn't get to zero first. Water has anomalous expansion so that it has maximum density at 4 deg C, which makes it freeze from the surface. That means that you can have one beaker with ice on the surface (0 deg at surface and 4 deg underneath before one that's at a lower temperature (1 deg homogeneous) if the one with ice in had some conditions that would cause the temperature gradient from top to bottom to be maintained.

The effect is real, but it seems that nobody can agree what it is and how it happens

Exactly.

Let's not forget water becomes less dense as it freezes not more. I have a feeling this effect may be linked to Brownian motion but so far I can't find a link which refers to that, so I'm probably barking up the wrong tree !

BTW any theory's on my observation of water droplets travelling up a wire ?

BTW any theory's on my observation of water droplets travelling up a wire ?

What was the weather like, was it windy?

BTW any theory's on my observation of water droplets travelling up a wire ?

it's called the capillary effect or adhesion. The wall of the wires are more polar than water, so water gets more attracted by the wires than by its neighbouring water molecules (attracted by neighbours = cohesion).

But will the water seed mod make much difference to your ebike?

it's called the capillary effect or adhesion. The wall of the wires are more polar than water, so water gets more attracted by the wires than by its neighbouring water molecules (attracted by neighbours = cohesion).

 

That's what you would imagine it would be but there are problems with that from what I can see.

As the water droplets moved up the wire they would merge with others, increase in size and eventually rush down the wire or just drip off.

I have a feeling this phenomena may have something to do with static charge on the wires...more research needed.

 

@ slarti.

Yes the water seed mod definitely works. If you're out on your bike and water droplets start to fall from the sky your speed increases by about 20% sometimes more. I would advise anyone who wants a quick speed boost to always carry a packet of Iodine crystals in their back pack.

“‘A pint of water weighs a pound and a quarter, a gallon weighs 10 pounds” pounded into me in primary school many years ago. It’s also why there are twenty fluid ounces in a pint. All UK measurements of course, USA gallons are different. 1 litre of water weighs exactly 1kg. Rounding errors in your conversion left you .0028lb out, not too shabby...