Kids Awkward Question corner – Solid, Liquid, Gas
Given the thread title and the usual interest of kids I was convinced this was going to be a thread about poo.
First person to mention water vapour then has to explain if that is ice, water or gas or why have you invented a new catagory of being.*
*She was a know it all 6 year old
You're donald ducked when she hears about plasma. I'd start reading things if I were you.
Also,
Water is weird and doesn't behave.
Ok, my go at this:
Water = H2O
Air = N2 and O2 plus other bits
Water is therefore lighter than air and would, without a force operating on it be a gas. As others have said the hydrogen forms weak bonds that generally hold everything together. However not all bonds are equal and a small increase in energy going in to the liquid (sunlight ambient, temperature, ground being warmer below the surface) can give so me molecules enough energy to break that bond and evaporate. In the open air this molecule is lighter than the air around it and it rises. As it goes up the temperature drops and if the molecule touches other molecules and they start to form a vapour. That is a loose collection of molecules that we see as clouds or mist.
This is the sort of “lies to children” concept that Terry Pritchett used that means that we simplify complex things in to stories that aren’t quite right, but you get the idea. The more complex explainations (which this may be depending on your audience) mean you loose people and they don’t get the concept, let alone the mechanisms.
It's odd that the assembled minds of the forum can't define the difference between solids, liquid and gas but your bumhole can with almost perfect accuracy.
Seems to me the problem in learning about this is the plethora of names we give water. Water, ice, steam, water vapour – four names for three phases. Confusion is understandable.
Folk talk about steam cos you can see it but it's not a gas. It's a different phase called an aerosol. There's loads of examples of substances that don't quite fit into solid/liquid/gas and they're usually colloids of some sort - that is little bits of one phase suspended in a continuous load of another phase. Aerosols are little bits of liquid suspended in a gas.
Colloids can be a bit counterintuitive and the physics of how they work can be tricky so we tend to leave them out of the model we start with for simplicity's sake. I don't think of this as 'lying to kids' btw, more 'how science works'. We ake some observations and come up with a model to explain/predict them. When we find stuff that doesn't fit the model we change/adapt the model to account for the new stuff.
It’s odd that the assembled minds of the forum can’t define the difference between solids, liquid and gas but your bumhole can with almost perfect accuracy.
You say that but, mine's made mistakes occasionally.
"Sorry love, back in a minute, I just need to go and check that last fart. I think it may have come with prizes."
You've all got it wrong, it's not evaporating, the fish are drinking it!
steam can be >100 degrees but water can’t
Liquid water can be >100 degrees. [ see superheating ]
This is the thing with teaching kids science, everything has to be simplified and exceptions to the rules ignored for brevity and easy recollection. The gaps get filled later. Teaching kids about the triple point of water after years of having 0 and 100 drummed into them as being when state transitions occur, must be a painful task. I wouldn’t want to be a teacher.
colloids
I’ve never heard that word before! Every day’s a school day.
Anecdotally, I read that the purpose of putting a pinch of salt into a pan of water, when cooking pasta, for example, is not for flavour.
It's because the disolved salt in the water raises the boiling temperature of the solution above 100c.
And that helps with cooking it better or something.
Thank you for listening to my TED talk.
Salt reduces the boiling point...it also reduces the freezing point, which is why it gets used on roads when it is looking like 0c temps.
It increases the boiling point as it is entropically unfavourable. You have to add loads for that value to be significant. You'd be better off increasing the pressure using a sealed container.
Whilst technically true, I can't imagine that a pinch of salt in a panful of water makes a significant difference to its boiling point. You'd be better off putting the pan lid on.
I Am Not An Italian.
I Am Not An Italian.
I bet you put Pineapple on your pizza too! 😉
The real reason to put salt in pasta water is to make the pasta taste better.
‘A pinch’ is vague. If you are cooking 500g of pasta in 5L of water you should add at least 25g of salt. More if you prefer.
I thought impurities typically lower the melting point and increase the boiling point of substances.
I’d imagine, but have not done the calculations or experiments, that 500g of pasta would have a bigger effect than 25g of salt on boiling point.
The melting/boiling changes assume you’ve not changed the ambient pressure or temperature between unadulterated/adulterated tests.
Maybe the pond has a leak....
What's the atmospheric pressure in the vicinity of this pond?
The thing about 100C is that’s the point at which the average energy of the water molecules is enough to break the bonds.
It is the temperature at which the pressure inside a bubble of gaseous water is equal to atmospheric pressure, so that bubbles can grow in shallow water and rise, aka boiling. So water boils at a lower temp at altitude and you can't make a decent cuppa. The pressure the bubbles have to overcome also has a component from the water pressure, so it takes higher temps to boil water at depth eg around hydrothermal vents.
There is also a weak component of pressure holding the water together/ tending to collapse small bubbles from surface tension (which is due to the hydrogen bonds). But that is not enough to keep liquid water drops intact in space, where water exists as ice. Unless it has a planet and atmosphere to provide the necessary pressure.
Ice in space is quite happy as ice because it's at absolute zero. It takes heat to change that hence the tail of a commet as it approaches the sun and warms up relaesign dust and gas which are carried behind it by the solar wind..
Ice in space is quite happy as ice because it’s at absolute zero.
It's actually 2.7 Kelvin in deep space. If you're in the solar system, it will depend how close to the sun and whether you are in shade or not. When the surface of the moon is exposed to the sun, it's above 100 Celsius, but when it's in shadow, it's about as cold as liquid nitrogen.
This was a concept that caused no end of difficulties as a primary school pupil learning about the water cycle. The idea of water vapour was beyond me. I got steam, but gaseous water in the air around us - no!
Later I found out what a difficult concept it was to teach.
Ice in space is quite happy as ice because it’s at absolute zero. It takes heat to change that hence the tail of a commet as it approaches the sun and warms up relaesign dust and gas which are carried behind it by the solar wind..
I knew that was not an ideal example to give, anyhow...
Water is also unhappy in space because liquid water cannot exist at low pressures (below the triple point pressure which is around 1/100 of an atmosphere), whatever the temperature. See the phase diagram below, off Wikipedia. If you could somehow transport a bucketload of water into space it would boil (though that word is possibly a bit peaceful for what would happen). The resulting bits would be ice and gas and would have some temperature. The lack of pressure would be the main driver of this, not coooling from the cold of space.
Water phase diagram the image wouldn't link
ETA of course if your bucket is planet-sized, then it can generate enough pressure via gravity for liquid water to exist, and it may also get warm enough somehow.
This was a concept that caused no end of difficulties as a primary school pupil learning about the water cycle. The idea of water vapour was beyond me. I got steam, but gaseous water in the air around us – no!
Later I found out what a difficult concept it was to teach.
I think it’s harder because we have special names for solid and gaseous water; harder still because we call the stuff that visibly comes out a kettle the wrong name. However I think that it makes sense if you ignore water for a moment and think of other liquids. We seem to get the idea that you can smell many liquids (without actually putting the liquid up your nose). It doesn’t take too much thought to imagine that this must be caused by some molecules leaving the bulk liquid and becoming vapour? Which can then reach our nose. Similarly we can all think of liquids that turn solid or vice versa. Glacial acetic acid would be an easy visualisation. Solid at fridge temp - liquid at room temp but clearly not boiling, yet you can smell it easily, but heat it up and it boils. It’s only because we don’t see, smell or otherwise observe water vapour that we forget it is there. Condensation makes it easy to show it is there though.
Water is also unhappy in space
water is a molecule (or if you mean liquid water a lot of molecules in close proximity) it has no emotions and thus the concept of describing it as happy/unhappy is actually weird. Sometimes it’s helpful to anthropomorphise atoms/molecules etc but it often leads to limits in our real understanding. The thought experiment of taking a bucket of water to space depends if you allow it to cool first or it boils before it’s cooled.
water is a molecule (or if you mean liquid water a lot of molecules in close proximity) it has no emotions and thus the concept of describing it as happy/unhappy is actually weird
@poly I am afraid the weirdness is mainly your's. As you later note, people do (often) anthropomorphise things. They are not all weirdos. Furthermore "happy" in such contexts is a common figure of speech, no doubt derived from ideas of what a human would feel but no longer indicating an actual connection with human experience. And further furthermore, thermodynamic happiness is true happiness. As for the thought experiment, it is clear. Water (I can't be arsed to keep calling it "liquid water" where the meaning is obvious) in space. What happens to it. You can't quibble about how it got there because it's a thought experiment. It just got there, all wet and bucket-shaped (the bucket may or may not still be present).
