Unfair dice

This is a model of an unfair dice. Depending on the model you choose, the dice has a hole beneath one (or more if you want) of its faces. This means that the face above this hole is more likely to come.

I use this in classrooms to introduce the idea of probability (law of large numbers). As a motivation, I ask the students to give which face is more likely to come up. Then I can check their predictions by throwing the dice in a cup of water (because of buoyancy and viscosity, the side with the hole will with nearly 100% of the time come up). Sometimes I add a couple of fair dices to make things more challenging. Note however that I found it hard to print a fair dice (but it might be due to my printer's poor accuracy). Defects in the geometry (e.g. the print direction or an uneven bed) have a big influence.

The hole is so designed that it can be printed in the upward/downward direction too (there is an inbuilt support in the design). This setting was important for me as I realised that most students notice in which direction the piece was printed, and try to infer that the hole might be there.

Be careful, depending on the parameters (in the customisation) and the fineness of the print, there might be visible holes.