When someone leaves an outside door open on a cold, still day, it is often said that the person is letting in cold air. If so, how

Diffusion

Explanation:

This process can be referred to as diffusion. The cold air moves from a region of high concentration (outside) to a region of low concentration (inside). The movement of these cold air is what is referred to as "letting in cold air".

NOTE: Diffusion is the process in which substances move from a region of high concentration to a region of low concentration. Just like when an insecticide is sprayed inside a closed room and then the room is later opened so as to allow the the sprayed insecticide leave the room.

explanation:

specific heat is the amount of heat required to raise the temperature of a unit mass of a substance.

freezing

deposition

condensation

explanation;

melting also called fusion is the process where solid becomes liquid, sublimation is the process where solid becomes gaseous without first changing to liquid, deposition involves change from gaseous to solid state, freezing involves change from liquid to solid, boiling or evaporation involves change of liquid to gaseous state, while condensation is the change from gaseous state to liquid state.

endothermic reactions involves absorption of heat from the surroundings or the environment while exothermic reactions involves loss of heat energy to the surroundings.

in this case, sublimation, evaporation and melting are endothermic reactions (gain energy from the environment) while, freezing, deposition and condensation are exothermic (loss of energy to the surroundings) reactions.