  In the present paper, we investigate the properties of the sound generated by
rubbing two objects. It is clear that the sound is generated because of the
rubbing between the contacting rough surfaces of the objects. A model is
presented to account for the role played by the surface roughness. The results
indicate that tonal features of the sound can be generated due to the
finiteness of the rubbing surfaces. In addition, the analysis shows that with
increasing rubbing speed, more and more high frequency tones can be excited and
the frequency band gets broader and broader, a feature which appears to agree
with our intuition or experience.
