 Alright, so why did this balloon inflate? Well, it turns out when you keep the empty glass bottle into the hot water, the hot water heats up the glass and that heated glass then heats up the air inside the bottle. As a result of which the air inside expands and we see that in the inflation of the balloon that inflates the balloon. So this activity shows that when you provide some heat to a gas, it expands. And this principle is followed in hot air balloons. In hot air balloons, there is a burner that you can see over here which heats up the air inside the balloon that makes the air very hot and lighter than the surrounding air which causes the balloon to rise. So you can arrive at the same principle that makes a hot air balloon rise. You can arrive at that principle in your classroom or in your home just by carrying out this activity.