Things have been quite quiet on the blog front, since the month of October was split asunder by a sneaky wee week off. Seven days in the arborial splendour of Center Parcs down Sherwood Forest way - some lesson planning being done between the archery, swimming, Turkish hamam and Kronenburg 1664. How do you make the concept of latent heat and change-of-state interesting to a bunch of 14 year olds ?
I settled on the idea of using reusable heat packs which use the latent heat produced by the crystallisation of sodium acetate gel. Preparation was good for me in that I had forgotten all about the whole change-of-state thing and the associated weird things that happen heat-wise.
Here's a wee query for all you armchair physicists: if I take two ice-cube trays - one with ice cubes and one with water - outside when the temperature is precisely zero degrees, what happens to the contents of each tray ? Consider this your homework for next week - answers on the comments page.
We're now on the semester-1 home straight. Back out to school for our teaching practice placement proper. This will last six weeks and will take us to mid-December and a three week holiday (which will be taken up writing a 3500 word essay due for January 7th). During this teaching block, we'll be responsible for three or four class groups delivering around ten lessons per week in total - which doesn't sound very much until you consider we're all taking around three to four hours per lesson plan. This three-four hours needs to become sub-60 minutes very quickly or it will very rapidly become completely unsustainable.
Also during this teaching block, every student gets their first "crit" - you are visited by your tutor who watches you deliver a lesson and then tells you why it wasn't very good. Essentially I have about three weeks to reach a minimum competency standard in time for the crit itself, and avoid the dreaded NYS grading. Not Yet Satisfactory.
Regular readers will recall that my two lessons so far were - in my opinion - NECTS and FB. Hopefully the latter will prevail in three weeks time.
The number of blogs over the coming month and a half will depend on how close I get to the sub-60 minute lesson plan, and how depressed I feel at not being able to do the job itself (which apparently is pretty much par for the course). I am fairly confident that by 14th December I will know two things about this career-jump of mine:
- Whether or not I enjoy teaching
- Whether or not I'm any good at it.
Here goes.
20 comments:
Is this a trick question? I do hope so. Here's my answer:
The ice in the ice cube tray will heat up to zero degrees, and remain as ice.
The water in the ice cube tray will cool down to zero degrees, and remain as water.
If you poured the zero degrees water into a glass (at zero degrees) and then dropped in a few of the zero degrees ice cubes, the ice cubes would hang around for ever and ever and never melt.
Do I win a prize?
So, zero degrees is neither the melting point of ice, nor the freezing point of water then ?
Are we to assume that 'outside' represents atmopsheric pressure? What happens will depend on the pressure.
If that's the case then at zero degrees then ice will melt and form water at the same rate as water is freezing to form ice. So I can't quite picture what's happening in each tray, but probably not a hell of a lot!
I do remember that H2O is the only substance for which the solid is less dense than the liquid...
On to much more important things... a programme about Gregory's Girl has just come on the telly...
Bella bella !
Ice at zero degrees will melt and become water at zero degrees providing that something (typically the outside temperature) is providing the latent heat of fusion (is that what it was called?) required to do do.
Similarly, water at zero degrees will freeze and become ice at zero degrees providing it's cold enough for the latent heat of fusion (is it still called that? Latent cold of fusion maybe) to kick in.
If the outside temperature is precisely zero degrees (at one atmosphere) then the latent heat to do either of the transformations isn't there - so the water stays water, and the ice stays ice.
I think.
I think that sounds about right.
Well, fusion is an exothermic process (it gives off heat) so you don't need to supply any.
Interestingly, my two physics tutors gave two separate answers to this, but we settled on my answer which takes account of the normal distribution of energies of the molecules. Basically we reckoned each tray would become an ice & water mix.
However as my bullshit add-on was fully enabled I'm not actually convinced.
Where's the boy Liddell when you need him ?
I think you've all got it covered!
Here's another for you:
You know a garden sprinkler? You fire water down a hose and as the water flies out the sprinkler spins?
Well, imagine you put the sprinkler in water under pressure so that the water rushes into the sprinker nozzle and back down the hose. What way does the sprinkler head spin?
So two tutors can't agree on the answer to what should be a basic physics question?
So much for that continuous improvement malarkey you were banging on about in posts passim.
Erm.....shuffles feet.....stares at ground.....
Um.
Aha - they're not teachers !
But if the water changes to ice AT THE SAME RATE as ice changes to water, then how can you end up with a mix? I still think the ice will stay as ice, and water stay as water.
...I mean, thinking about each tray individually.
I think the mix will occur because there isn't a clear push either way, a zero degrees it is at the margin, and it all goes fuzzy.
Its like clouds. Why are there clouds in the sky? Is water a vapour at atmospheric pressure?
Anyways, in answer to the underwater sprinkler scenarion - won't the sprinkler head just stay stationary ?
Re: the sprinkler - I'll make an ill informed guess that at the ends with the open nozzles (where the water is rushing in) the moving water will be at a lower pressue than the opposite end, and so it'll spin that way.
Have I won the prize for most comments against a single blog ?
The points for the sprinkler thing go to Mr. Gordon, it doesn't move, the water enters the nozzle from all directions so the forces net themselves out.
It was a puzzle that troubled Feynman so he built an apparatus to try it. The first attempt, the glass jar he used exploded all over a computing lab.
Hey that must mean I'm cleverer that Feynman then !
Probably.
Nah. Just cleverer than me.
Now there's damning with faint praise...
That's quite enough of your ingrained Catholic inferiority complex young man.
Spot it a mile off.
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