three shadows object

This nice object casts 3 different shadows: a circle, a square and an equilateral triangle (the 3 Bauhaus essential shapes). It's important to note that this is theoretically truth only when light rays arrive in parallel (which requires a punctual source of light infinitely distant). In practice Sun rays will do the job perfectly, whereas artificial lights won't.

There are many more objects, often more complex than this one, that cast interesting shadows. Check, for instance, this one: https://www.thingiverse.com/thing:202774

Also very famous is the EGB objects, featured in the book cover Gödel, Escher Bach, and found among the examples in OpenSCAD.

(I printed a version with some rice on it (I used a straw to slide the rice while printing) and made a nice maraca).

Overview and Background

This nice object casts 3 different shadows: a circle, a square and an equilateral triangle (the 3 Bauhaus essential shapes). It's important to note this is theoretically truth only when light rays arrive in parallel (a punctual source of light infinitely distant). In practice Sun rays will do the job perfectly, whereas artificial lights won't. There are many more objects, some more complex that this one, that cast interesting shadows. Check, for instance, this one: https://www.thingiverse.com/thing:202774 Also very famous is the EGB object, featured in the book cover Gödel, Escher Bach, and found among the examples in OpenSCAD. Education-wise, I think this object can be revisited in different grades and for different purposes. From K to 12. For instance: big kids or adults will find very challenging to design an object that casts these 3 different shadows, it's a great design/geometry problem that requires process-thinking.

Lesson Plan and Activity

As mentioned, one interesting activity is to ask students to design an object that casts 3 different shadows; and then later these particular 3 different shadows. Also interesting is to try to let students explain why with artificial lights the shadows are not perfect polygons, what fails?

Materials Needed

Print the object, wait for a sunny day! Also: play with artificial lights to see why it fails. If the challenge is to design and build such object, one approach is using soft wood, clay or basically any construction material. Another is using a 3d design software. Tinkercad is perfect.