# A Few Questions

davegage
Posers and Puzzles 24 Apr '05 04:12
1. 24 Apr '05 04:12
1. Why are man-hole covers always round (cylindrical)?

2. At 1 atmosphere of pressure, you cool a beaker of water to 0 deg C, but it does not freeze. You cool it to -10 deg C, still doesn't freeze. You cool it to -20, -30, -40 deg C, respectively. Still it doesn't freeze. Why not? (Pressure is held constant at 1 atmosphere throughout.)

3. The sum of Eve and Ann's ages is 44. Eve is twice as old as Ann was when Eve was half as old as Ann will be when Ann is three times as old as Eve was when Eve was three times as old as Ann. How old is Eve?
2. 24 Apr '05 05:09
1. So it won't fall down the hole.
2. The water is highly pure, and it is super-cooled
3. 24 Apr '05 07:17
1. They aren't
4. Alcra
Lazy Sod
24 Apr '05 12:18
Originally posted by davegage
1. Why are man-hole covers always round (cylindrical)?

2. At 1 atmosphere of pressure, you cool a beaker of water to 0 deg C, but it does not freeze. You cool it to -10 deg C, still doesn't freeze. You cool it to -20, -30, -40 deg C, respectively. Still it doesn't freeze. Why not? (Pressure is held constant at 1 atmosphere throughout.)

3. The s ...[text shortened]... hen Ann is three times as old as Eve was when Eve was three times as old as Ann. How old is Eve?
1. A round object cannot be turned such that it can fit through the hole - a square one can.

2. Is it a trick question? The beaker does not freeze? If you mean the WATER does not freeze, I give up.

5. Acolyte
24 Apr '05 13:181 edit
Originally posted by PawnCurry
2. The water is highly pure, and it is super-cooled
How hard is it to get this to work? Do you need laboratory conditions? I want to get my hands on some supercooled water. You could flick a tiny speck of dust in and watch an big ice crystal grow extremely rapidly around it.

Actually I did read something in New Scientist once, about someone who ordered a bottle of fizzy minral water from a restaurant. When they opened the bottle it fizzed a bit and then suddenly froze solid - a) because the pressure went down slightly, b) because the CO2 content went down and c) because the bubbles provided ample nucleation sites which hadn't been there before.
6. The Plumber
Leak-Proof
24 Apr '05 15:09
On many occasions I've put a bottle (plastic) of water into the freezer - I like my water cold when I drink it - and then left it in longer than I intended. If the water is pure enough, it's still liquid when you take it out. A little shake and - voila! - you have ice crystals throughout; usually it's slushy when that happens. I've also very carefully set the bottle down and removed the lid - ice crystals begin to form at the top and you can actually watch them propogate to the bottom of the bottle - take 3 or 4 seconds. Of course, if you leave it in the freezer too long, you just have a bottle of ice....

When I was in high school we did an experiment in chemistry where we heated up a sugar water solution (distilled water), and dissolved more sugar in the water than it can hold on room temperature. We then allowed the solution to very slowly cool to room temperature - the sugar stays in solution so that you have a super-saturated solution. We then dropped a single sugar crystal in the center of the solution and watched the sugar crystals form almost instantaneously.

(And yes, you can try this at home)
7. 25 Apr '05 23:53
Originally posted by Acolyte
How hard is it to get this to work? Do you need laboratory conditions? I want to get my hands on some supercooled water. You could flick a tiny speck of dust in and watch an big ice crystal grow extremely rapidly around it.
Select a small, clean drinking water bottle. Drill its cap so as to allow
insertion of a thermometer. Seal the thermometer at the cap with a
suitable sealant -- silicone, perhaps. Fill the bottle with distilled
water. Screw on the cap and allow the water to stand undisturbed for a
day. Without shaking the bottle, place it on a freezer so you can see the
freezing zone of the thermometer. Allow the bottle to stand in the freezer
for several hours. Check it from time to time -- do not move the bottle or
agitate it in any way.

If all goes well, the water will cool to below its freezing point (32 F, 0
C) as evidenced by the thermometer reading of (perhaps) -2 C. The water
inside the bottle has supercooled.

Remove the bottle from the freezer, shake it gently for no more than one
second, and sit it on the lab bench. The water will suddenly start to
freeze solid.

You will note that the temperature will rise as the water freezes. Extra
credit: How can this be? Why does the temperature rise while the water is
freezing?