This conversation between Socratic-minded parents and children was reported in The Science Creative Quarterly.
OLDER CHILD: Remember that car we saw when we were walking to school, with the vapor coming out of its tailpipe?
YOUNGER CHILD: I made vapor come out of my mouth, too. It was cold.
FATHER: What do you suppose that vapor was that came out of the tailpipe?
OLDER CHILD: Was it steam?
MOTHER: Sounds good to me.
YOUNGER CHILD: Why was there steam coming out of its tailpipe?
FATHER: What is steam?
OLDER CHILD: Gaseous water.
MOTHER: So why would a car have gaseous water coming out of its tailpipe?
OLDER CHILD: Maybe there was water in the fuel tank?
FATHER: Can you think of any other reason?
MOTHER: What’s the fuel people usually put in the fuel tanks of their cars?
YOUNGER CHILD: Gasoline!
FATHER: That’s right.
OLDER CHILD: But how does gasoline end up making steam come out the tailpipe?
MOTHER: Do you know what the car has to do with the gasoline to get the energy out of it?
YOUNGER CHILD: No.
MOTHER: It has to burn the gasoline.
YOUNGER CHILD: Like a fire?
FATHER: Yep. And do you remember what a fire needs to burn?
OLDER CHILD: Oxygen!
MOTHER: That’s right.
FATHER: So, do you remember what happens when we light candles and then let them burn all the way down?
YOUNGER CHILD: They melt!
MOTHER: But if they just melted, all the wax that started out in the candles would end up dripping onto the table. We get a few drips, but not whole candles’ worth of drips.
OLDER CHILD: What happens to the wax?
YOUNGER CHILD: Yeah, where does it go?
FATHER: Let’s see if we can figure that out. (Grabs a tealight candle, a 4 ounce canning jar, and a lighter.) OK, I’m lighting the candle. What will happen if I lower the jar over the candle?
OLDER CHILD: The flame will go out!
YOUNGER CHILD: (As the flame does go out) It ran out of oxygen!
MOTHER: That’s right. So that must mean that the oxygen gets used up when something is burning.
FATHER: (Relighting the candle) What if I lower the jar more slowly so the oxygen doesn’t run out so quickly? Can you see something forming on the inside of the jar?
YOUNGER CHILD: Is that wax?
OLDER CHILD: Steam! It’s steam!
FATHER: That’s right. So, burning uses up oxygen …
OLDER CHILD: And makes water!
MOTHER: Do you know what else is produced when you burn something?
OLDER CHILD: Carbon dioxide.
YOUNGER CHILD: How do you know that?
OLDER CHILD: I don’t remember. I must’ve heard it somewhere.
FATHER: So, if burning the wax uses up oxygen and makes carbon dioxide and water, what can you say about what the wax is made of?
MOTHER: (After some blank looks) What is carbon dioxide made of?
YOUNGER CHILD: Carbon and dioxide.
OLDER CHILD: Carbon and oxygen.
MOTHER: And what’s water made of?
OLDER CHILD: Hydrogen and oxygen.
MOTHER: And you know that oxygen is getting used up when you burn the candle — the oxygen that goes to make the water and carbon dioxide.
OLDER CHILD: So the carbon and the hydrogen come from the wax?
FATHER: Yep. Wax has carbon and hydrogen, and so does gasoline.
MOTHER: Hydrocarbon fuels. And the foods your body burns for fuel have carbon and hydrogen in them.
OLDER CHILD: Like carbohydrates?
FATHER: And fats, and proteins.
YOUNGER CHILD: We burn our food?
OLDER CHILD: And sometimes have tailpipe emissions.