The Q Mystery
What to do
Click and drag the yellow pattern so that it overlaps the purple pattern. Or click and drag the purple pattern over the yellow pattern. What do you see?
Think about it
The new pattern you see is called a Moiré pattern, formed when two patterns partly overlap. The lines and spaces of varying thickness combine to form a new pattern.
Two layers of flywire or mosquito netting can form Moiré patterns. You can also see these patterns when looking at a glass window through a fly-screen. The fly-screen and the reflection of the fly-screen combine to make a new pattern.
If the fly-screen is perfectly even and the glass is perfectly flat, the Moiré patterns will be very regular. If the pattern on the screen is even slightly uneven, the Moire pattern will be very uneven. Because of this, Moiré patterns can be used to check that objects are flat, or evenly curved.
Scientists and doctors have used this idea to devise a simple method to detect scoliosis, an abnormal curvature of the spine. As strong light passes through a frame of horizontal black threads onto the back of a patient, a Moiré pattern is formed! If the pattern is not symmetrical, the spine is curved or deformed.