Newton's Disc is a well-known experiment used to demonstrate the properties of light and color mixing. It's a disc that is divided into segments, and each segment is painted with one of the colors of the visible spectrum, similar to the colors seen in a rainbow.

Understanding Newton's Disc and Color

The concept behind Newton's Disc is related to how our eyes perceive color and the phenomenon called persistence of vision.

• Visible Spectrum Colors: The disc typically contains the colors Red, Orange, Yellow, Green, Blue, Indigo, and Violet. These are the colors that make up white light when combined.
• Persistence of Vision: This is the ability of the human eye to retain an image for a fraction of a second after the object is gone. When images move rapidly, our brain merges them together.

What Happens When Newton's Disc Rotates?

When you look at a stationary or slowly rotating Newton's Disc, you can clearly see the individual color segments. However, as the disc starts rotating faster, something interesting happens:

As the disc rotates at a high speed, the colored segments move past our eyes so quickly that the image of one color persists while the next color segment is already in view. Due to the persistence of vision, our brain doesn't see the individual colors separately anymore. Instead, it blends all the colors together.

The Appearance of a Fast Rotating Newton's Disc

According to the principles of additive color mixing (how light colors combine), when all the colors of the visible spectrum are mixed together in the right proportions, they produce white light.

Since Newton's Disc has all the colors of the spectrum arranged correctly, when it rotates very quickly, the colors combine visually in our perception. This rapid mixing of all the spectrum colors results in the disc appearing to be almost white.

It appears "almost white" rather than perfectly white because achieving a perfect white requires precise proportions of each color and a perfectly uniform surface, which is difficult to achieve with paint on a physical disc.

Therefore, the colour of the fast rotating Newton's Disc appears to be almost white due to the mixing of the spectrum colors caused by the persistence of vision.