Answer:
1. Cool air is more dense than warm air so it sinks to take the place of the warm rising/buoyant air.
Explanation:
This is why heating a room with cold outside walls or glass windows (if budget can afford), we use warm radiant heaters at the floor level to break up the convection current/cold draft.
As opposed to just diffusing air at the ceiling level, which is good in summer as cool air falls (air conditioning is in range of 55 to 65 degf out of the diffuser), mixing with warmer room air.
