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3.3. Fracturing

How To Invent (Almost) Anything > 3. A Simple Science Lens > 3.3. Fracturing

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For some surfaces, the problem with lack of smoothness is overcome by the fact that molecules or even lumps of molecules will crack and break off as you move objects against each other. If you start sanding a piece of wood the first push may be hard but it soon gets easier as the surfaces are broken down to become smoother. The bits that are broken off also fill the holes, serving as an added lubricant; it is only when you blow the sanded wood particles away that you find out how truly smooth the wood has become.

Thus another way to increase or decrease friction is to find ways in which you can increase or decrease the ease of breaking off small pieces of surface. Making things colder or hotter is one way, as this will change the brittleness of the materials. A special example would be ice, as this is complicated by the fact that the ice will melt in places to give you a liquid lubricant.

Fig. 3.3 Fracturing pieces to smooth and reduce bounce

The first three features of friction we have discussed (bounce, elasticity and fracturing) are to do with larger mechanical forces. These can be understood simply by drawing rough surfaces on a large scale and asking yourself what happens to objects moving past each other. For the next three features we are going to move closer in to the molecular level.

Other sections in this chapter:

• 3.1. Bounce
• 3.2. Elasticity
• 3.3. Fracturing
• 3.4. Electrostatic Action
• 3.5. Viscosity
• 3.6. Gravity
• 3.7. Invention 'So What'?

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