Bobby McFerrin

The above video is Bobby McFerrin (the Don't Worry Be Happy guy) showing off some important music science. But why does it work?

Bobby is having the audience sing along the pentatonic scale. (In the wikipedia article, Bobby is using the major pentatonic scale.) One reason this scale is so ingraned in us is that it's used in a variety of folk music. Many children's songs use the pentatonic scale, such as Oh Suzanna.

The pentatonic scale also sticks in our minds because it's easy to hear -- it's made up of tones that we're used to hearing.

The Ancient Greeks did the math a long time ago to figure out that these pitches lie on a harmonic series. If you pluck a string, it makes a sound. We'll say the sound is C. If you divide the string up, you start getting different pitches. Half of the string will make another C, but a third of the string will make G, which is one 5th up from G (C D E F G -- there are five notes inbetween C and G.) If you divide THAT string into three parts, you'll get D. (G A B C D -- G and D are fifths.) Divide THAT string into three parts, you get an A. (D E F G A -- D and A are fifths.) Divide THAT string into threee parts, you get E. (A B C D E -- A and E are fifths.)

Arrange all these pitches into alphabetical order, you get C D E G A, which is the C pentatonic scale.

You can learn more about the harmonic series here. It has a good diagram explaining all that Greek string division.

This link talks more about constructing a pentatonic scale by using fifths, and it has good pictures, too.