WHich one is true?

[paperfairy]

From what I know, heat rises.

However, the higher the altitude, the colder is gets, as seen on mountain tops and in Pokémon episodes (lol, PKMN physics).

So does heat rise, or not?

 

[The Incarnation ポケモン]

Heat doesn't rise. Heated AIR (and water) rises. At high altitudes, there isn't that much air to begin with. Hence.

 

[The Big Al]

You've come to the right place.

Hot air does in fact rise. This is due to the fact that hot whatever is less dense that the same substance at a lower temperature.

What you are talking about is the state of our atmosphere. Air Pressure decreases with elevation. This means the density decreases. Since heat is the net motion of molecules, the less molecules you have in a given volume the less heat can be generated and therefore the lower the temperature.

For the record, above the troposphere in stratosphere we have an inversion where the temperature does increase with height. However, this is because of the chemical reactions of ozone being subjected to ultraviolet radiation.