|MadSci Network: Earth Sciences|
Good question, Adam,
The reason air is cooler at higher elevations than at lower elevations is because air pressure decreases as you get higher. In other words, the higher you drive up a mountain, the less air there is to press down on you. Even though it is hard to imagine, air has weight just like anything else.
When air pressure gets lower, the air becomes less dense and therefore cools down. On the other hand, when air pressure rises, air becomes more compressed, and heats up.
Maybe your teacher can bring a can of aerosol hairspray to your class as an experiment of how this works. You will notice that the can becomes colder as hairspray is released and the pressure in the can decreases.
You can also experiment with an ordinary balloon. Air inside a filled balloon has higher pressure than air outside the balloon. When you release the air from the balloon onto your skin, the pressure lowers and the air feels cool on your skin.
Thanks for the question!
Try the links in the MadSci Library for more information on Earth Sciences.