Question

Why does milk ebullate on heating?                                                                                                              Why is the temperature fairly constanew for landmasses surrounded by large water bodies?

Answer 1

The answer to both questions is  convective currents or convection.

When milk is heated from below, the hotter milk particles rise to the top of the liquid because they become lighter. Then the milk which is colder on top due to its higher density goes down.  This form of heating liquids is called convection.  When boiling point of milk (at the  atmospheric pressure) is reached the water particles in milk take heat from the neighbouring molecules and escape in to the air.  So the cooled milk particles from near the open surface go down to the bottom.  This process appears ebullient very vigorously at the boiling point.

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Do you mean   overflow over from the top of the utensil to outside.?

Certain dissolved substances in milk come out as gas on heating of milk. The gases coming out from inside the milk, lift the creamy layer on top of the milk air boundary. The creamy layer on top of the milk is formed by the fats inside the milk.  The gases coming out of milk expand due to heat and so lift the creamy layer.  Milk bubbles formed due to surface tension are able to rise to the brim of the utensil.

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This effect is due to convective air currents.

Landmasses near water bodies do not have very large difference in temperature between day and night.   During the day landmasses get hotter due to the radiation from the Sun.  Their specific heat capacity is lower than that of water.  So water heats up slowly absorbing most of the radiation falling on the water body.  So during the day time, the temperature of the air on top of water body is lower than that on the land mass.  Hence, Cooler air (denser and of higher pressure) from the water body blows towards the hotter air region on land due to less pressure there.

Similarly, in the night, the landmass cools down quickly due to lesser specific heat.  So the air on the landmass is cooler and denser.  Hence the air pressure on top  of land is higher.  Where as, on top of the water body, the air is hotter because the heat is dissipated by water slower than land.  Thus the air currents start blowing from the land towards the water body. Due to these currents, the temperature of landmasses increases.