A simpler way to think of convection would be that cold air is heavier (more dense), so they have to be at the bottom, and hot air is lighter (less dense). Imagine if you have a heater placed on the floor, sadly your feet will always feel cold as the hot air rises
This way of thinking is particularly useful when you are dealing with MCQ questions on convection.
Not sure if anybody has talked about this, but sound waves require a medium to travel through! This is a classic question which appears in MCQ almost every year ...