Hot air rises because:
A hydrogen balloon rises in air because
Hot air always rises up.
The mercury in a thermometer rises when it is placed in hot water because ______.
Hot air rises, while cold air descends.
Ventilators are provided near ceilings in the rooms of our houses because:
1. Hot air is lighter than cool air.
2. Hot air rises up and cool air settles down.
3. Hot air is heavier than cool air.