Final answer:
Steam fills the bathroom during Greg's hot shower due to evaporation, where the water turns from liquid to gas. The heat from the shower provides energy for this transition and causes convection currents, which circulate the steam throughout the bathroom.
Step-by-step explanation:
When Greg took a hot shower, the steam filled the bathroom because the water vapor from the shower mixed with the air. This phenomenon is an example of the physical process where water changes from its liquid state to gas due to the heat from the hot shower. This process is known as evaporation and is accelerated by the high temperature of the water which provides energy for the water molecules to transition to the vapor phase.
The steam rises and fills the room due to convection currents, a process by which heat is transferred by the movement of fluids (in this case, air). Warmer air rises above cooler air because it is less dense, thus leading to the circulation of steam throughout the bathroom. Additionally, when water evaporates, it requires heat which it takes from its environment, causing cooling, but in the case of a hot shower within a bathroom, the continuous supply of heat from the hot water maintains the temperature and causes more steam.