What is necessary for a convection cell to be set up in a fluid? a) changes in density b) thermal gradient c) thermal gradient and changes in the density

Convection cells don't work in solids.

In order for convection to happen, material with some temperature and density has to FLOW to a place where the material there has a different temperature and density.

Material doesn't FLOW in solids, only in FLuids.

car a and b are moving in opposite directions

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c because the action was the roller coaster reaches bottom of hill (action) reaction would be blood tends to drain away from head

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