Storm8 said:Hi this is probably very easy for you guys, but I can't figure this out. Heated air rises right? Then why is it that when I put a bowl of soup in the microwave and heat it in a plactic Tupperware-like container, then remove and cover it -- does a vacuum like effect occur? It would seem to me tha the hot, steamy air would want to push the cover off. Instead it sucks the cover down. Why?
This is the same reason as to why airbeds can be completely inflated at first but seem to loose air throughout the night. I strangely worked this out in a semi-dream state recently (before looking it up to confirm it). I went away for the weekend and stayed at a friend's on the Friday, his house was well heated and the airbed was fine all night. On Saturday I stayed at a different friend's on the same bed but this friend's house was much colder, halfway through the night I woke up on a partially deflated bed. In my half-dream state I concluded that if it had a puncture it would have deflated all the way and that the inbuilt pump must heat the air it pumps through, thus because of the cold air it had seemed to deflate.mathman said:Once you remove it no more air is added. As the air cools down the volume reduces (ideal gas law) - so it sucks down.Storm8 said:It would seem to me tha the hot, steamy air would want to push the cover off. Instead it sucks the cover down. Why?
mathman said:Once you remove it no more air is added. As the air cools down the volume reduces (ideal gas law) - so it sucks down.
I suspect both factors (water condensation and air cooling) play a role. I'll leave it to others to quantify.Lsos said:That's what I thought at first, but I think a larger reason for the effect is that as it cools, the steam inside the container condenses into water. The volume of water is something like 1000x less than steam, so it greatly reduces the pressure inside the container.
When the soup is heated, the fact that hot air rises plays a small part trying to lift the lid. However, a larger part is played by the increased pressure inside, again due to water turning into steam.
Lsos said:That's what I thought at first, but I think a larger reason for the effect is that as it cools, the steam inside the container condenses into water. The volume of water is something like 1000x less than steam, so it greatly reduces the pressure inside the container.
When the soup is heated, the fact that hot air rises plays a small part trying to lift the lid. However, a larger part is played by the increased pressure inside, again due to water turning into steam.
The vacuum effect in hot soup is caused by the difference in temperature between the soup and its surroundings. As the soup heats up, the molecules in the soup start moving faster and spread out, creating a lower air pressure at the surface of the soup. This lower air pressure then pulls the surrounding air towards the soup, creating a vacuum effect.
No, the vacuum effect in hot soup is not dangerous. It is a natural phenomenon that occurs due to the properties of heat and air pressure. However, if the soup is extremely hot and spilled, it can cause burns, so it is important to handle hot soup with caution.
Yes, the vacuum effect in hot soup can be reversed by either allowing the soup to cool down or by breaking the seal between the soup and its surroundings. This can be done by stirring the soup or blowing air over the surface of the soup.
Yes, the type of container can affect the vacuum effect in hot soup. A container with a smaller opening will create a stronger vacuum effect compared to a container with a larger opening. Additionally, a container with a tight-fitting lid will create a stronger vacuum effect compared to a container with a loose-fitting lid.
Yes, the vacuum effect in hot soup can be utilized for other purposes. It is commonly used in food preservation techniques such as canning and vacuum sealing. The vacuum effect can also be used in chemistry experiments and as a teaching tool to demonstrate the effects of heat and air pressure.