Placeholder Image

字幕表 動画を再生する

  • (gas hissing)

  • It's not often that

  • I think of an experiment for Periodic Videos

  • where I really want to know the answer,

  • rather than just having a regular demonstration.

  • Today, I thought of one of those experiements.

  • There is quite a well known effect

  • -known as a fuel-coolant interaction-

  • where a molten metal

  • drops, say, into water and causes an explosion.

  • And we've sort of had some of those

  • in some of our videos

  • with caesium and sodium in water;

  • But there you have a metal which gets hot through a chemical reaction.

  • I had suddenly thought:

  • Why don't we try dropping mercury

  • into liquid nitrogen

  • because mercury is hot, it's room temperature

  • liquid nitrogen is at -196° C

  • The hypothesis is that because the metal conducts heat so well,

  • the heat will come out very quickly and there'll be a

  • *woosh*

  • as all the nitrogen vaporizes.

  • The experiment was done in three stages.

  • So first of all: Liquid nitrogen with solid copper.

  • Same temperature as the mercury but because it's solid

  • there's no change in surface area,

  • it can't break up into small droplets

  • so it should be safer.

  • So you put it in and much to our pleasure

  • it really looked quite nice.

  • (ethereal music)

  • So, that part at least was safe.

  • But just to be doubly sure

  • he then dropped the mercury the first time

  • into a really big vessel

  • so that even if there was splashing and so on

  • none would come out.

  • (ethereal music)

  • The thing that particularly pleased me was that

  • when the mercury froze, because the freezing point of

  • mercury is -40° C,

  • there were quite nice crystals that you could see formed

  • on the surface of the metal

  • and there was this great lump of mercury at the bottom

  • solid.

  • But Neil had quite a lot of difficulty getting it out

  • at the end and it began to melt and so on.

  • But that wasn't part of the experiment

  • Then came the real experiment:

  • A small vacuum flask

  • where you can see inside without condensation

  • on the surface from the vapor pressure in the air

  • and he dropped in the mercury.

  • What's interesting is that as it goes into the liquid nitrogen,

  • the nitrogen boils, and so the mercury falls

  • almost encased in this little bubble

  • of nitrogen gas.

  • Then, when it gets to the bottom it goes

  • *splat* on the bottom, spreads out,

  • and then the transfer of heat

  • becomes much more violent

  • and there is a huge upwelling.

  • Mercury going this way,

  • and bubbles of gas going up.

  • (gaseous boiling sounds)

  • As an experiment it was really nice

  • it looked really good.

  • I'm not completely convinced that it demonstrates

  • how well heat is transferred from a liquid,

  • but you can see that it's far more violent

  • than when you drop in a lump of copper

  • because the surface area of the mercury

  • is much, much larger

  • and the heat travels out through the surface

  • through the interface between the liquid nitrogen

  • and the metal

  • So, I think

  • in the end, we have demonstrated the point.

  • That even with a difference of just over 200° C

  • you can get quite a violent boiling

  • Imagine now if you put in really hot mercury

  • if you put in boiling mercury into liquid nitrogen,

  • then you might get really quite a bang.

  • You might even break the vessel.

  • (Brady: Are you going to let us do that one, professor?)

  • Well I'd be happy for you to do it

  • Neil would not be happy,

  • we would smash his vessel

  • and he'd have to clear up the mess as well.

(gas hissing)

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

液体窒素に水銀を注ぐ(スローモーション (Pouring Mercury into Liquid Nitrogen (slow motion))

  • 1 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語