Describe an activity to demonstrate that warm air is lighter than cool air.
i) Take two same sizes of empty paper bags.
ii) On the two ends of a wooden stick hang the both of bags in an upturned position.
iii) In the centre of stick tie a portion of thread.
iv) According to the figure (A), hold the stick by the thread in balance.
v) According to the figure (B), place the burning candle below one of the bags.
vi) Now, you will observe unbalanced stick. This represents that as the warm/temperate air rises up and it pushes the bag over the candle.
vii) Now we can say that when air is heated, it expands and also occupies more space. So, we can conclude that warm air is lighter as compared to cool air.