I had some nice soup tonight

[Begram]

It was Tescos butternut squash. Yummeee

You're supposed to heat it in a bowl, but I microwaved it in the plastic tub it came in, since there was only half of it left. It got really hot!

I couldn't be bothered mixing it with a spoon, so I just swirled it around in my hand. The whole thing started collapsing, like a vacuum pump had been attached. What's that all about? I thought the air would get hot inside and expand?

[rojash]

I'm assuming you heated it with the lid on. If so what happened is that when you heated it, the air expanded and forced its way out around the lid seal. After you took it out of the microwave, it started to cool, and the remaining air contracted, but this sucked the lid on tighter, so no more air could be taken in to replace that which had been forced out. Hence, the internal air pressure was now much lower than that of the atmosphere and the pressure differential was enough to crush the container.

[Begram]

sorry no. The lid was off when I cooked it. When I reattached the lid, nothing happened. When I swirled, it started contracting very fast.

[mr_pointment]

another word of warning Begram never ever bake your conkers in the microwave to make them hard they could explode

[gen2]

Begram, What rojash says still applies. You placed the lid on when it was very hot and steamy. The lid prevented any more air from entering and as the air within cooled, contracted and water condensed, it created the reduced pressure that caused the effect you saw.

I remember an experiment at school where a small volume of water was placed in the bottom of a one gallon metal can and heated to boiling over a bunsen burner. Once the steam had driven most of the air out, the flame was removed and a screw cap was tightened on the top. As it cooled, air pressure crushed the can to a distorted, flattened wreck. That is the effect you noticed with your soup.

[Begram]

I hear what you're saying, but honestly try it the way I did it...it's not the cooling. It didnt' contract when stationary. When swirled, it contracts the more you swirl it. Why is this? The swirling would probably heat the air, anyway.....

[rojash]

Sorry it's such a boring answer, Begram, but the fact remains that it's just the cooling. After the air has been forced out, most of the gas left in the container is water vapour, at a higher temperature than the soup. When you swill it around, you just accelerate the process of distributing the temperature more evenly amongst the contents. The liquid gets fractionally warmer, the gas gets a little cooler and condenses, leaving a potential vacuum. At that point the container is crushed by the pressure differential.

[Begram]

sorry, rojash, but I don't think that's it. The container is half full of air, waterladen maybe, but half full of air. The container does not suck in at all, until the swirling begins. Either the air pressure lowers in the container, or the movement deforms the plastic such that it distorts and collapses the container.

[Begram]

actually, the air is substantially cooler than the liquid, and the pressure differential is between two different matter states, liquid and gas...they just do not interact by pressure differentials to produce this effect.

[Begram]

I have just tried this with water, same tub, instead of soup. It has the opposite effect, blowing the lid off. The soup is butternut squash on a largely vegetable stock base. This is getting intriguing now...

[Creepy]

You must be mad heating food in a microwave fullstop. heating foods in plastics that hot is a recipe for disaster ! (no pun intended)
Try real food - its safer

[Begram]

what, like 'beef'?

[rojash]

Sorry begram, but you just don't want to know the mundane truth - you want some exciting mystery. The reason you got a different experieince with the water is simply that you heated it to a higher temp. When you agitated it it boiled. If you had waited a little 'til it was the same temp as the soup, the container would have collapsed in exactly the same way.

[Begram]

Hi Rojash, thanks for the petty insult.

You happen to be wrong.

Sorry begram, but you just don't want to know the mundane truth LEAVE IT OUT. - you want some exciting mystery. LEAVE IT OUT

The reason you got a different experieince with the water is simply that you heated it to a higher temp. WRONG, THE SOUP WOULD BE AT A HIGHER TEMP THAN THE WATER. EVEN SO, WHAT DIFFERENCE WOULD IT MAKE????????

When you agitated it it boiled. REPEAT THIS TO YOURSELF AGAIN SLOWLY. 'WHEN I AGITATED IT IT BOILED. WRONG.

If you had waited a little 'til it was the same temp as the soup, the container would have collapsed in exactly the same way.
WRONG.

Try this out and actually think about the science, before you come back with another guess as to what is happening. Not nice to be wrong, especially when you're giving it the big 'I'm write, you refuse to accept my infallible majesty.'

My life would be so much better if I would only believe everything that passed Rojash's lips.

[mibn2cweus]

In spite of popular opinion microwave ovens heat from the top down, mostly on top. Soup is viscous so that convection currents like those when heating water are reduced. By sloshing, the cooler soup on the bottom cools the sides of the container. I believe rojash can (and has) explained the rest.

[Begram]

It's soup....the heat will have distributed quite evenly. The sides are polyethelyne. It is hardly changed at all by sloshing.

I think rojash is totally wrong, but I can't be arsed going through it. What happened to all the scientists on this site?

[Fat Boy]

The AnswerBank - where you post a question and then argue with all the answers you get until someone that agrees with you.

It was the magic soup fairies that made it happen. Happy now?

[Begram]

Science is NOT about providing answers: that is RELIGION. Science is about providing reasoned explanations based on evidence. In this respect, the above answers are NOT scientific, and thus I reject them. I do not accept an answer just because the person providing it feels confident in it. You may want to check out 'History and Myths' Fatboy.

[mibn2cweus]

Polyethylene shrinks when heated. Mystery solved. Your welcome.

[Begram]

/\A reasonable answer consistent with the evidence. Read and learn.

[Genesis]

Erm, sorry to throw a spanner in the works and I am by no means a technical person but, if the answer is that the polyethylene shrinks when it is heated, why didn't it do the same when you tried the experiment with water, or are you saying that with the soup the sides caved in and the lid was sucked down, but that with the water, the sides still caved in but the lid was blown off?

*slopes off into corner to await an ear-bashing.....*