Answer:
density; thermal
Explanation:
Convection currents occur in fluids because of temperature and density differences. Convection currents transfer thermal energy throughout a fluid.
<em>When a fluid is heated, the molecules closest to the heat source gets heated first and their temperature is raised. The rise in temperature lowers their density and as such, they move to the upper portion of the fluid to be replaced by yet-to-be-heated molecules at the upper portion. </em>
<em>When the replacement molecules also get heated, the same process occurs and a to-and-from rotational movement of molecules, also known as convection current, is created within the fluid. The to and from movement, thus, transfer thermal energy within the fluid until all the molecules within the fluid are at the same temperature.</em>
