warm air cold air

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It's really hard to teach kids about molecules. They can't see them, so they don't believe they are there. When I used to work at a science museum, I asked a lot of kids what "things" are made of. The most common answer was ANTS! Cute, but soooo incorrect. I hope this quick and easy activity will help you teach your little ones something about molecules, or at last prove to them that molecules do exist. The basic concept here is about the behavior of cold and warm air molecules. Cold air molecules stay packed together. They don't have as much energy as warm air molecules, so they don't take up as much space. Warm air molecules have more energy. They bounce around a lot more, taking up more space.

Materials:

• 2 liter plastic bottle with cap removed
• balloon (the round kind, not the long skinny kind...trust me....)
• freezer
• warm sunny spot or toasty hands

Put the bottle in the freezer for a few minutes. When you remove the bottle, place the balloon around the opening. The balloon should be completely deflated. Quickly place the bottle in a sunny spot or have your child hold it with both hands. As the air inside the bottle gets warm, the balloon expands and stands upright.

There's a lot of teaching you can do with this activity. My hubby uses it to teach about weather. For example, there's not a lot of humidity during cold winters - the cold air is more dense and can't hold as much water vapor. Warm air molecules bounce around a lot, leaving space between them to hold water vapor. You can also teach about conduction if you have your child hold the bottle. Conduction is the transfer of heat energy from a region of higher temperature (hands) to a region of lower temperature (bottle from freezer). Lastly, you can discuss convection. Do any of you have a convection oven? Convection is the movement of heat energy through fluids (like liquids and gases). In this cases, it's the movement of the air inside the bottle. Remember the saying "hot air rises"?