Place a pyrex funnel with its mouth-down in a sauce pan full of water, in such a way that the stem tube of the funnel is above the water or pointing upward into air. Rest the edge of the bottom portion of the funnel on a nail or on a coin so that water can get under it. Place the pan on a stove and heat it till it begins to boil. Where do the bubbles from first? Why?




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This question is not very clear.  I am not sure i understood the question clearly...   
Please see the diagram.

   The funnel ABC is inverted and is positioned leaning over a small block in a pan containing water.  The water is boiled.  So the bubbles arise from the bottom of the pan (and from the water in the middle too).  The surface S1 of the mouth is lifted higher than the surface S2 on the RHS of the center of mass O of the cone.

   There is a buoyancy force associated with each air bubble rising to the top.  Some bubbles hit the surface S1 and some bubbles hit the surface S2.  The Bubbles will have the same volume at the same pressure.  Radius of the bubbles rising is inversely proportional to the depth below water surface.  Radius is inversely proportional to the differential Pressure (inside bubble to outside the bubble).

   To me it appears that the net total torque T1 on the surface S1  will be more than that torque T2  on Surface S2.  So the funnel will lift upwards from the side A rather than side B.

   Bubbles will come out from end A, rather than from end B.  Of course bubbles will come out from the stem tube at C.  Because many bubbles glide along the surface S1 and S2 and from the middle of mouth of funnel rise through the stem tube.

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