What is convection ?

Answer 1

Take this example
when you put some fire
the hot air tries to get up.
Which is against gravity.

When you are boiling the water the water at the bottom get warmed soon and as it get warmed it pushes the water above it which is a bit less warm.

The net motion turns the warm water moves upward and the less warm water goes down.
This phenomenon is called convection
it is not seen in absence of gravity.

It is a kind of transfer of energy which comes into play due to gravitational pull over.

Answer 2

Convection is the movement of heat by the movement of a fluid, (liquid or gas)
When an area becomes warm, it rises because it is less dense.Cool air or water flows in to replace that which has raised and then it is warmed and raises. A convection current is formed .
This is seen as soup warms on a burner, at the seashore as seen in sea breezes during the day and land breezes at night, cool air flowing down out of an open refrigerator, warm air rising from a hot drink, or a radiator.

Answer 3

Sometimes a single physical process in nature can explain a variety of events. Convection is one such process. It functions because heated fluids, due to their lower density, rise and cooled fluids fall. A heated fluid will rise to the top of a column, radiate heat away and then fall to be re-heated, rise and so on. Gasses, like our atmosphere, are fluids, too. A packet of fluid can become trapped in this cycle. When it does, it becomes part of a convection cell.

Convection cells can form at all scales. They can be millimeters across or larger than Earth. They all work the same way. The convection that students are most likely to have observed is in cumulonimbus clouds or "thunderheads." These towering vertical clouds can be seen to evolve over a few minutes. The tops of the clouds have a sort of cauliflower appearance as warm moist air rises through the center of the cloud. The moisture in the cloud condenses as it cools. The air gives up some of its heat to the cold high altitude air and begins to fall.

As the air falls along the exterior of the cloud, it returns to warmer low altitudes where it can be caught up in the rising column of air in the center of the cloud. This fountain-like cell can form alongside other cells, and a packet can move between cells. Hail forms when water droplets, carried by the strong updrafts, freeze, fall through the cloud and are caught in the updraft again. An additional layer of water freezes around the ice ball each time it makes a trip up through the cloud. Eventually, the hail becomes too heavy to be carried up anymore, so it falls to the ground. Large hailstones, when cut apart, show multiple layers, indicating the number of vertical trips the stone made while it was caught in the convection cell.

Answer 4

Convection is movement or circulation of a liquid or gas.

Answer 5

heat carried by a moving medium (eg air or water)

hot air rises (less dense)