Kids and Combustion

When I was in high school, I remember friends who were jealous that my parents knew math and science – since obviously that meant I could ask them for help with my homework. What my friends didn’t know was that my parents treated the most straightforward question as an invitation to a freewheeling Socratic dialogue of no less than 30 minutes. While I would have been happy just to finish my assignment with time to watch some TV, my parents wanted me to understand how things worked.

Isn’t it funny how we do to our kids the very things our parents did to us?

Our children are five and seven years old. They do not yet regard the Socratic method as a species of regrettable parental behavior. Although perhaps this is because, on occasion, we also play with fire.

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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?

MOTHER: Soot?

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.