Naturally, my kids ask, “why is the cold air denser than warm air?”
There is no end to their curiosity, and I am rather thankful for it! This is how little engineers and scientists are created!
As the air warms, the molecules move faster and further apart. As a result, air expands and becomes less dense.
We can see the effect of heating up air with this simple hot and cold balloon experiment. Your kids will love watching the balloon blow up and shrink by placing it in hot and cold water!
How to Inflate a Balloon with Hot Air
- Ice cubes
- 2 containers
- Empty water bottle
1. Blow up the balloon a few times to stretch it. It will help the balloon inflate with the hot air.
2. Pour water in one container and add ice cubes.
3. Pour hot water in the other container. The water doesn’t have to be boiling, just hot from the tap.
4. Place the opening of the balloon over the mouth of the empty water bottle.
5. Place the water bottle in the hot water. Watch the balloon inflate!
6. Place the water bottle in the cold water. What happens to the balloon?
This science experiment is easy to set up and plenty of fun for the kids. They were so surprised when the balloon first inflated when we placed the bottle in hot water!
We tried both using a regular balloon and a water balloon. While both balloons inflated, the water balloon stood straight up while inflated due to its small size. You can use either to demonstrate how the warm air expands inside the bottle and blow up the balloon.
Then we saw how the balloon quickly deflated when we place the bottle in the cold water. The air molecules when cooled contracted, took up less space, and the balloon collapsed.
The beauty of this experiment is that you can do it over and over again! Just add more ice cubes if all of them melted, and heat up more water once the warm water cools.
To understand more about how air behaves, make sure you check out the warm air rises, cold air sinks experiment.