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Why does my tea blow up? :-)

  1. Apr 18, 2007 #1
    Hello, I'm new here.
    I hope I do not offend all of you physics gurus with my simple question. Here is the scenario:

    I have a Rubbermaid 2.5 liter container that I like to fill up with hot (boiling) water, 3 teabags and few spoons of sugar. I'm not sure what kind of plastic exactly it is, but it does not melt or shrink like a regular PET bottle. It is pretty sturdy. When I close the lid and shake the hot tea inside to make it mix with the sugar, pressure builds up inside and (occasionally) pops open the lid. I usually release the steam inside before it does this.

    Can anyone explain why this is happening? What happens to the steam as it get agitated?

    Thank You! :smile:
  2. jcsd
  3. Apr 18, 2007 #2


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    The water's hot, near boiling. You put it in a bottle with a little cool air, close it, and then rapidly heat the air to nearly 100 degrees C by shaking the bottle. The air expands, and increases the pressure inside the bottle until the lid pops open.

    - Warren
  4. Apr 18, 2007 #3
    I see. Thanks. For some reason I thought the air above the water would get heated too (at the instance of me pouring the hot liquid in the container). I did not realize it takes time to transfer heat to a layer of air.

    So when I mix it, the exchange surface area between the tea and air increases dramatically and helps to speed up the heating --> expansion of the cooler air.

    I wish I was a little brighter ;-) Thanks chroot!
  5. Apr 19, 2007 #4
    I think the lid pops up because of high pressure alright. But the high pressure is mainly due to the steam, not only the air. In the formula PV/T =constant, T here changes not very much because you have to use the Kelvin scale. You have to add with 273 K so you compare T1=273+25 and T2 =273+90, the ratio T2/T1 is not very high surely (appr. 1.2)
    The reason here is that when you shake the container, you increase the phase boundary between water and gas so it accellerates the steaming process. The water vapor of course will build up pressure and pop up the lid consequently.
    You can test this very easily. After the lid has been popped off, you put it on and shake the container again. Probably the lid will pop out once more if the water is still hot enough.
    Last edited: Apr 19, 2007
  6. Apr 19, 2007 #5


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    Because, when you mix up the tea that way, you make tea 'n' tea!

    <sorry, couldn't resist>
  7. Apr 19, 2007 #6


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    I'm ashamed to say that took me a couple of seconds, but now I'm quietly giggling to myself...:rofl:
  8. Apr 19, 2007 #7
    Funny!! :P
  9. Apr 19, 2007 #8
    Good to see some wit in these here forums. :smile:
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