Watch what happens in this video of a Newton colour wheel:

Did you see? When the wheel speeds up it appears white. When the wheel slows down, the colours reappear. Why?

Isaac Newton is responsible for this theory - as well as the theory of gravity, his three laws of motion, the reflecting telescope and calculus. He definitely kept himself busy!

Isaac Newton

Before Newton, nobody knew that visible light was made up of seven different colours. People thought that light was just 'light' and that colours were a mixture of light and darkness. They thought that bright red was 'light' with just a little bit of 'darkness' and that deep blue was pretty much all 'darkness'. But...they were wrong!

Have you ever seen a small rainbow on a wall in your house or school? This is formed when light is bent (refracted) through a prism (a glass object with flat, polished surfaces). The prism causes the visible light to bend, or refract. The violet light is bent more than the red and yellow light, so the colours separate. These colours - all the colours of the rainbow - make up visible light.

Visible light bent (refracted) by a prism (cc) WebExhibits

Newton used a prism to split up light into the colours of the rainbow and project the rainbow onto a wall. To prove that the prism wasn't colouring visible light, he then used another prism to refract, or bend, the light back together again. This caused all the colours to merge back together into what we call visible, or white, light. Pretty impressive, right?

Newton colour wheel

A similar thing happens when you spin a Newton colour wheel. When the colour wheel spins rapidly, the colors merge into each other very fast and our brain is not able to distinguish between the different individual colors. So, what do you get when all the colours of the rainbow are merged together? White (or visible) light!

Why not make the colours of the rainbow disappear with a New ton colour wheel and amaze your friends and family?

Go to: /categories/experiments/magic-tricks/2010/12/can-you-make-a-rainbow-disappear.aspx

Or use the physics of density to create a rainbow in a glass by going to: /categories/experiments/messy/2012/10/liquid-rainbow-in-a-glass.aspx