The law of conservation of mass states that in a chemical reaction mass is neither created nor destroyed. For example, the carbon atom in coal becomes carbon dioxide when it is burned. The carbon atom changes from a solid structure to a gas but its mass does not change.
So that they know what the world is about and that they become aware of what is happening out or what will happen if they do certain things.
Multiply the length times width times height
Mount Everest. Just because it wasn't found yet doesn't mean it didn't exist.