When it was his turn, he got up and pulled something out of the bag next to his chair. Literally: he pulled it out of the bag.
Open with a hook, they had said. So he decided to open his lesson on functions with a visual prop: his grandmother’s meat grinder, which he pulled out of the bag and fastened to the table as a social studies teacher, an artist and a recreational sports manager watched patiently.
“We’re going to talk about functions,” he said.
Who knows what they thought.
“The idea of functions is simple,” he said. “Like this meat grinder, they take some input, they do something, and then they generate some output. Functions are just little machines that convert inputs into outputs. This meat grinder is a function. It takes chunks of beef as input and generates ground beef, hamburger as its output. Or it takes turkey in and generates ground turkey out. Or pork in and ground pork out.”
And then they did some worksheets, putting pencil to paper. They worked with other functions. Functions that given state names as inputs return capital cities as outputs. Illinois in, what comes out… anybody? That’s right: Springfield! And of course more math-y functions like one that takes number as input and returns that number incremented by one as output. Five goes in, six comes out.
And so he was off and running. Having opened his lesson with a solid hook, he was teaching them about functions. It seemed to work well.
But here’s the thing about that meat grinder. In a way it was perfect — a literal example of an input-output engine. But having used it as a prop, he couldn’t get over wondering what a pain in the neck is must be to have to clean that “function” after every use — something for which he had no mathematical analogy.