brake cables and drip coffee machines

A while back, I had what might be called an epiphany of ignorance. In such a situation, what makes the sudden insight so mind-broadening is the realization that one has lived for so many years on this planet in complete ignorance of a simple aspect of everyday life. In this instance, a colleague at work said he was pretty sure that the plastic housing around bicycle brake cables have metal coiled around the inside. Being naturally argumentative, I started to disagree without having given the issue a moment's thought. Eventually I started to come around, and we eventually figured out that there has to be a push on the housing to balance the brake lever's pull on the inner wire, with confirmation from an informative website on bicycle minutiae. The author says it is all about Newton's third law ("every action has an equal and opposite reaction"). Being Newton's Ocean and all, I have given this rather too much thought, and I have come to the conclusion that it is more to do with the need to balance forces so that an object compresses rather than undergoes a bulk acceleration.

If we start by imagining a centre-pull style front brake, just pulling on a bare wire should work as long as you are sitting firmly on the seat, so that a force is also transmitted downwards to keep the front of the bicycle from lifting upwards. In principle, I suppose one could still end up lifting the front of the bike right off the road that way, so the use of a reinforced cable housing to transmit the necessary downward balancing force along the same path as the upward pull on the brakes via the inner wire makes more sense! Plus it allows the cable to bend and still transmit a differential force between the inner and outer components. It also allows for less symmetrically designed brakes such as side-pull and linear-pull systems, where the inner wire is connected to one side, and the balancing compression force from the housing is applied to the other side.

So there you have it. The other day, this same colleague confided that he sometimes pours day-old coffee into the reservoir of our communal drip-style coffee machine, in order to reheat it. This led to a discussion about whether this would gunk up the machine, which led to a debate concerning how exactly such a machine works! The issue was whether the water would boil and deposit any residue in the reservoir. Now I kind of knew that the water didn't get totally turned into steam, but how does it move up the tube to get to where it drips down onto the coffee grinds? It turns out that pockets of steam and a one-way valve ensure that the heated water moves against gravity up the tube.

Perhaps the real epiphany is how much clever stuff there is in the "simple" things around us.