Have a look at this picture of a chessboard. There is a cylinder
placed on the board which is casting a shadow:
Look at the squares marked A and B.
Do you think they are the same colour or different colours?
Show this image to some other people. Perhaps you could ask other
children in your class, or members of your family.
What do they think? Are the squares the same colour or different
Keep a record of how many people think they are the same and how
many think they're different.
When you've asked, say, 10 people (you might be able to ask more),
have a look at your results.
What percentage of people you asked thought they were the
What percentage thought they were different?
Now, have a look at this picture
(It will open in a new window.)
This new image shows the same chessboard and cylinder, but now the
squares A and B are joined by two strips which are the same colour
at all points.
What do you think now? Are squares A and B the same colour as each
other or not?
Show this new picture to the same people you showed the first one
What do they think? Are the two squares the same colour or
Do any of them change their mind compared with their first
What percentage think they are the same now?
If you look at this second set of data you've collected, does it
persuade you to change your mind?
How could you convince yourself and others that the squares are the
same colour or not?