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Last week I did an expermient which goes as follows, I boiled some amount of water, and then put in a small piece from an uncooked thread of noodle, first of all it went right down to the bottom of the boiling vessel stayed there a while and then came back up. One would obviously think that when first it sank why it rose now ?

On watching carefully I observed that the small piece of noodle was covered with air bubbles, it was like someone had wrapped it in bubble wrap and let it float on the scalding water. Now the question comes that why did the bubbles accumulate around the noodle such that it started floating ?

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  • $\begingroup$ the bubbles come from the dissolved air in water... $\endgroup$ – shortstheory Oct 25 '13 at 12:43
  • $\begingroup$ I know where they come from the question is about why they are helping a fellow noodle particle to rise with themselves $\endgroup$ – Rijul Gupta Oct 25 '13 at 13:06
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When water starts to get hot, a lot of bubbles will form down the walls of your container. These bubbles are air. water has a lot of air dissolved on it. Then, as the boiling point of water is reached (100 degrees Celsius or 212 degrees Fahrenheit), water vapor starts to form inside the liquid in the form of bubbles (boiling point of water and its vapor is in equilibrium).these water vapor bubbles will start to rise to escape due to less density than liquid itself. A piece of noodle is denser than liquid water, so it drops down to the bottom of the vessel. Soon after it reaches to the bottom it starts to cook outside in. which means, it will start to absorb boiling water and start increasing its size, the escaping air bubbles sticks to the noodle piece due to higher surface energy. When the buoyant force of the noodle increases due to air bubble stuck to it, it starts to rise to the surface and floats.

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  • $\begingroup$ I do not have much knowledge of all concepts here, so can you explain why bubbles would stick to somethint having higher surface energy ? $\endgroup$ – Rijul Gupta Oct 25 '13 at 13:08
  • $\begingroup$ This video should help you to understand easier.please do let me know if you have any more doubts.youtube.com/… $\endgroup$ – Vaishakh Rajan K Oct 25 '13 at 15:28
  • $\begingroup$ Same reason as water droplets can stick to something, really. $\endgroup$ – MSalters Oct 25 '13 at 16:05

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