What you need:
Two round Styrofoam plates, a pair of scissors, a friend
What to do:
1. Nest the two plates together and using the scissors, cut out two arcs from the sides of the plates. The plates being one under another ensures that both arcs are of the same length.
2. Hold up the arcs separately, one above the other. Make sure that one of their ends are lined up. What do you see?
3. Now, interchange the arcs; the top one now is at the bottom and vice-versa. Is there a change?
4. Ask your friend to look at the arcs as well.
What happens:
The arcs appear to be of different sizes! The arc held above always appears to be smaller, although you know for a fact that both arcs are of the same size (since you did the cutting!).
Why?
When we hold the arcs above one another, our eye starts comparing the inner curve of the arc above with the outer curve of the arc below.
Naturally, the inner curve looks smaller.
This is an optical illusion, one in which the segments of a circle appear to be of different lengths if they are held one above the other, with one of their ends lined up.
You can ask your friend to make the pair of arcs equal using the pair of scissors and keep interchanging their places. Your poor friend can go on until nothing but small squares of Styrofoam are left!
Picture Credit : Google
