The inverse relationship between time and frequency is easily seen graphically. We often say that a function which is wide in one domain is narrow in the other, and vice-versa.

For example, in the plot below, vary the width of the Window function (in the time domain) and notice the inverse relationship of its Fourier Transform, the Sinc function (in the frequency domain).
(Drag the left waveform directly on the plot.)

To see this in a free-standing window, click here: 

Send comments to Dr. John Glover at glover@uh.edu .