Nature is full of rough surfaces - a flame front in a combustible material, a drop of coffee spreading on a napkin, or the surface of a growing crystal. However, the so-called kinetic roughening of surfaces can only be partially explained by existing theories and computer models. Now Jussi Maunuksela from the University of Jyvaskyla in Finland and colleagues have carried out detailed experiments on the motion of combustion fronts in different types of paper and revealed a range of new behaviour that shows how little is really known about these problems (Phys. Rev. Letts. 84 1946).
The group studied three different weights of paper in their experiments. Sheets of paper were place in a combustion chamber and lit by an electric wire. The propagating front of the fire was recorded by three CCD cameras. Each pixel recorded by the camera was smaller than the individual fibres in the paper, which allowed high resolution data to be collected.
The Finnish team then plotted the speed, depth and distribution of the combustion wave. According to the data, some formulae such as power laws – could describe the propagation of the wave fronts on short time and distance scales, but no existing equations or model could predict their behaviour on longer scales.