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3.2. Elasticity

How To Invent (Almost) Anything > 3. A Simple Science Lens > 3.2. Elasticity

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When two objects try to move against each other, if one has parts which will move elastically then it may effectively reduce resistance as the flexible parts of the surface bend around and over the bumps on the other surface rather than having to bounce over them.

Consider pushing a heavy box across a wooden floor. The box bounces along awkwardly with plenty of frictional resistance. If we took a piece of carpet, turned it upside down and put the box on top, now the flexible hairs on the carpet would fit into the gaps between the bumps, smoothing the ride and making the box easier to push.

Fig. 3.2 Using elasticity to smooth the ride

Now consider what would happen if we now had to push the box (with the carpet attached) across a carpet. The two sets of hair in the carpet would now entangle, actually increasing the friction. The algebra of this is as follows:

Bumps + Bumps = Friction
Bumps + Elasticity = Less friction
Elasticity + Elasticity = More friction!

To increase or decrease friction, consider the elasticity in both surfaces. Think about how easy or not it is to move a vacuum cleaner around the house. Over carpet, a smooth metal plate would be the best bottom surface, over a smooth floor a bristle surround would be better. The whole picture is complicated by the fact that you have air flowing between the surfaces, but the principles are clear. (Note: This an example of a contradiction, as will be described in Chapter 5. You sometimes want smooth and you sometimes want fibrous/rough surfaces.)

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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