COMSTOCK PARK, Mich. — Rising air is all around us— outside and inside. It's what meteorologists call "convection." Warm air is lighter and less dense than cold air, so it has buoyancy and wants to rise. This experiment helps demonstrate that. Keep in mind, low pressure systems generally create rising air. When the air rises, it cools, condenses, and clouds and precipitation can form.
On a much smaller level, and inside a third grade classroom at Pine Island Elementary in Comstock Park, we demonstrated this rising air motion. It's a simple experiment that can be done anywhere with just a balloon and plastic water bottle and some hot water.
Stretch a balloon over an empty plastic water bottle. Put some hot water in another container, then submerge the water bottle with the balloon in the hot water. There's air already in the bottle, but it's room temperature. Nothing happens to the balloon until submerged in hot water. The air is slowly heated inside the bottle, then begins to rise. It's invisible so you can't see it, but you can witness the effects of it. The balloon will slowly pop up and very slightly inflate as the warm air rises into the actual balloon. This is similar the way a hot air balloon works. Burners send hot air into the balloon and inflate it.
The balloon won't completely inflate simply because there's not enough pressure, but you can see the change. Once the bottle is removed from the hot water, the balloon will deflate as the air slowly cools.