# Physics problem.Only logic,no formulas.

1. Oct 2, 2011

### Elaia

In a dish we pour water.We boil it for some moments.Then we turn off the oven and the water gets colder.The boiling is interrupted.If we pour cold water outside the dish (in contact with it) the boiling starts again.WHY does the boiling start again???????

2. Oct 2, 2011

### Pengwuino

It wouldn't. Why on earth would it?

3. Oct 2, 2011

### BobG

Is this the result of an actual experiment?

I could see it happening provided the water in the dish were very near boiling. Boiling temperature depends on the atmospheric pressure.

The lower the atmospheric pressure, the lower the boiling point of water. For example, water always boils at a lower temperature at high altitudes (and many recipes vary their quantities/procedure slightly for high altitude). If you were boiling water right before a storm hit, the water would also boil at a slightly lower temperature as the air pressure dropped.

If pouring the water on the outside of the dish created a local low pressure area over the dish, then water that was just barely below the boiling temperature could start boiling again. Of course, the dish would have to be made of a material that insulated very well, so that pouring cold water on the outside of the dish didn't immediately lower the temperature of the water inside the dish. In other words, if this did work, I wouldn't expect it to work for long.

4. Oct 2, 2011

### sophiecentaur

I have to ask whether the experiment is reliably repeatable or a one-off.

5. Oct 3, 2011

### Aaron William

Say the dish is metal - would the thermal contraction create a rougher surface and more nucleation sites?

Grasping at straws here.

Last edited: Oct 3, 2011
6. Oct 3, 2011

### sophiecentaur

I see you have used the word "oven". What kind of oven? Did you open a door to add water? What material was the lower dish made from? What was the oven temperature?
One of these details (or another) may give us a clue, I hope. Can you describe the whole thing nor fully?

7. Oct 3, 2011

### Phrak

It is not in general true that cooling the outside of a container will cause the water to boil.

However, under some restricted conditions this can happen, as Bob alluded. See the You Tube video.

Last edited by a moderator: Sep 25, 2014
8. Oct 3, 2011

### Staff: Mentor

Calling mythbusters ......