Help and Critique needed: GSP file

Hello friends.

This is what I've been doing this afternoon. It's a Geometer's Sketchpad file that I hope to use with my calc class when we talk about volumes of revolution. I tried to upload it using Javasketch for those of you that don't have GSP, but found out that JavaSketch doesn't support function plots, or pretty much anything I used to create the sketch. Typical.

Anyway, I'm looking for feedback. Play with the sketch, press the buttons, see what you think. Ideally, I'd like this to be along the lines of a Dan Meyer "What Can You Do With This" type activity, but I don't think I'm there yet.

It's not finished, mainly because I don't quite know how to create functions for the last 1.5 pictures. Any help is appreciated! Thanks, friends.

A new version is posted here. Thanks to iTeach in the comments section (@PersidaB on twitter) for coming up with cubic regressions for the lasat 2 pictures. I didn't think to use my graphing calculator...wanted to do it all in GSP and couldn't figure it out. Thanks again! More feedback is always welcome, too. :-)


  1. I think I may have figured out a function for your last one. I will email you... I plotted points and did a cubic regression. The r^2 came out to .995.
    I LOVE the investigation. I am trying to do something like this later this year in my honors geo classes - to get them started on visualizing this way. I hope you don't mind if I "steal" parts of it.

  2. I love it too. Thanks for sharing.

  3. I don't know how I saw it in 2010. I don't have geometer's sketchpad. I don't suppose you have a way to show it for those of us who don't have the program? I'm teaching volumes right now, and am very curious...

  4. Maybe you could save it to google drive and open it with (free) Sketchpad Explorer on the iPad?