This applet demonstrates Fourier series, which is a method of expressing an arbitrary periodic function as a sum of sine and cosine terms. In other words, Fourier series can be used to express a function in terms of the frequencies (harmonics) it is composed of.
This example is a sawtooth function. The white line is the sawtooth, and the red line is the Fourier approximation of it. Adjusting the Number of Terms slider will determine how many terms are used in the Fourier expansion. Move the mouse over the white circles to see each term's contribution, in yellow. Low-frequency terms are on the left; high-frequency terms are on the right. You can also modify the function with the mouse.
Click the Sound checkbox to hear the sawtooth wave.
Next: Square Wave