This video sets up the puzzle and asks some questions about the behaviour of the tube.
Questions to investigate:
• Why do you only see one colour (symbol)?
• Why do you see exactly 3, 4 or 5 spots?
• What would you see if you looked up through a glass table?
• How would it differ if you put the one symbol on the bottom of the tube and the other on top?
This video gives an explanation of the behaviour of this trick so don't view it until you have done your own investigating.
The tube length should be cut to be exact multiples of the diameter. For example: a 21 mm PVC pipe should be cut to be 5 x 21 mm = 105 mm to generate 5 spots when spun. Smaller diameter pipes are more difficult to spin.