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# Trammel of Archimedes, Snap, Ellipsograph, Ellipse, Math, Model

by lgbu Dec 6, 2017

### Thing Apps Enabled

This looks really cool, I'm going to print one for my kids' math teacher.

As far as I understand it, the eccentricity of the ellipse is controlled by the spacing of the holes. Your design has just one arm with fixed spacings. Do you have any idea how much that spacing can be varied (I guess how far can the 'middle' hole be moved) and the device still work smoothly?

I will give a try modifying your arm by punching out multiple positions for the 'middle' hole, and if it works well, post it as a remix.

Thanks for the comment. You are right about the eccentricity of the resulting ellipse. Essentially, the longer the arm (distance from the 2nd hole to the pencil hole), the smaller the value of the eccentricity. Of course, you can make the arm longer and then add more pencil holes. One can also change the distance between the two holes for the sliders. Typically, I use this as a "model to equation" problem for students at secondary or college levels. I have attached the worksheet with 2 proofs. Do feel free to play with the relative distances between the holes. Have fun! lgbu