Be careful what you plot

Today in Calculus, I was waxing euphoric about why what we’re about to embark upon is amazing — how we’re eventually going to be able to find volumes and surface areas of strange figures. Not your standard spheres or cylinders or cones, but strange, exotic figures.

So I decide to open WinPlot and produce a surface created by revolving around the x-axis.

As I pressed “Enter” to generate the graph, I immediately recognized that we were going to have a problem. But it was too late.

revolution

I could have picked any number of other functions, but I decided to pick \sin x. Great.

We all had a laugh. Ah, high schoolers.

Moral: Be careful what you plot in class.

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4 comments

  1. @Kate: That’s amazing. yeah, the physics teacher at my school avoids using the terms “rod” and “ball” – the 9th graders can’t handle it

    This particular incident extended into today. In my MV Calculus Class, we were learning how to do revolutions about an axis by using parametric equations with 2 variables (u and v).

    So if f(x)=x^2, we can write x(u,v)=u; y(u,v)=u^2 cos (v); z(u,v)=u^2 sin(v), and these equations define f(x) revolved around the x axis.

    Of course I wanted to graph one on WinPlot to show my students, so I said “pick a function, any function” and of COURSE, one of the students says “SINE OF X.” I started laughing so hard, telling them “very funny guys…” assuming they had talked with students in my Calculus class. The best part is — they hadn’t. So I had to tell them the story AND graph it AGAIN today.

    Great times. Great times.

  2. Oh, no, you walked right into that one. That’s something they don’t teach you in credentialing programs. Revolved sine curves look like boobs. Yet another argument for experience in the classroom.

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