Question

How can you prove hot air is light and rises up?

Answer 1

We can prove hot air is light, and that it rises, by the following activity:

Take two large paper bags and tie them to the two ends of a ruler with strings. Now, tie a piece of string at the centre of the ruler, so that the ruler is balanced on both sides. Next, place a lighted candle below one of the paper bags and observe. The experimental arrangement is as shown below. We observe that the balance of the bags is disturbed.

Inference: The balance of the bags is disturbed because the air inside the bag gets heated up by the candle. As the air heats up, the particles in the air move further apart from each other. Therefore, hot air is light and rises upwards, causing a disturbance in the balance of the bags.

Conclusion: We can conclude that hot air is light and rises up.