Mindboggling

[unixronin]

Last week's weather was really ugly at times, and in particular, we had one night when it rained, then snowed, then rained, then snowed ...  It ended up with the driveway covered several inches deep in slush too heavy for the snowblower to shift.  Then the slush froze, leaving an ice crust thick enough to drive on.  I wound up, in desperation, hooking up the hosepipe to a hot-water faucet to get the ice off the driveway.  (This wasn't as absurdly energy-intensive as it sounds.  The ice was spongy, and melted very rapidly under a strong jet of hot water.

While I was doing this, one of our neighbors said, "You know hot water freezes faster than cold water, right?  Try it in your freezer sometime, put an ice tray of hot water and one of cold in there, and the hot water will freeze first."

I was so gobsmacked I just didn't know what to say.  I've heard some ridiculous urban legends in the past, but this one ... I just don't know where to start.  Where on earth does anyone get such a totally wrong-headed idea?  It falls down on even the very simplest of examination — the hot water's got to get cold before it can freeze, and that's going to take time, so the only way the hot water can freeze faster is if some cold water freezes faster than other water, but how do you know you didn't get magic fast-freezing water out of the cold tap in the first place?  To freeze before the water that started out cold, with both trays being cooled at the same rate, the hot water would have to cool to the starting temperature of the cold water in negative time.

Snopes is silent on this one.

The only way I can think of that someone could "prove"this to themself is if they inadvertently put the tray of hot water right under the cold-air inlet to the freezer compartment, so that it's being much more strongly cooled than the other.

Comments

[unixronin.livejournal.com]

Interesting ... but this looks like it's an effect that they can reproduce some of the time under some conditions, and no-one can really figure out why. I have to speculate that in some way they're haven't yet recognized to take into account, the conditions of the two are not equal. I see they've tried repeating it with degassed water, and that they've calculated evaporation can't be enough to explain it. I wonder what happens if both are stirred to neutralize the difference of convection currents in the water?

It's so counter-intuitive and ass-backwards it makes my brain hurt just thinking about it.

[skellington.livejournal.com]

Yeah.

I'd heard the "old wives tale" when I was a kid, went through the same thought process you did, and did an experiment in the kitchen freezer. (2 trays of ice, one with hot, one with cold.) The hot took longer to freeze and I wrote it off.

But it is a commonly known fact that it does occur, and there's plenty of scientific evidence now to support it.

[tabbifli.livejournal.com]

Your freezer self-defrosted. :)