If you see a hot air balloon is rising above the top of the hill what is the top of the hill called

The answer to your question is,

The top of the hill is called the reference point. As you can reference the top of the hill as where you are. :)

-Mabel <3

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.