Once Works Well was pure technology. Now it seeks merely to divert.
Pansy subjects - Verse! Opera! Domestic trivia! - are now commonplace.
The 300-word limit for posts is retained. The ego is enlarged

Friday, 22 August 2008

Not magic, just hard work

In one Olympic sport competitors appeared to flout the laws of a branch of physics known as mechanics.

Remember I said “appeared”. But here’s how. Getting a stationary car to move off requires lots of power (called torque) from the engine. But the engine develops most torque when it’s revving. To ensure the car can move off even on a steep hill (highish engine speed) and subsequently run quickly but economically (lowish engine speed), a gearbox is inserted between the engine and the back wheels.

Same with a bike. Mine has fifteen speeds, giving me the technical wherewithal – if not, alas, the requisite leg power – to cycle away easily and deal with any gradient.

But the bikes of Chris Hoy, Bradley Wiggins, et al, at the vélodrome didn’t have gears. Since they often crossed the finishing line at 70 kph where did the compromise occur? If the rider can cycle away from a standing start why aren’t his legs an impossible blur at maximum speed?

The answer lies in the riders' thighs – Hoy’s are like tree trunks. The bike’s single gear is unbelievably high and most of us would be incapable of getting going, let alone riding up the banked track. Not our goldmeisters though. The high gear serves them well during sprints when the legs move up and down quickly but controllably.

All you need to create the illusion of defying physics are huge thigh muscles. Or, funnily enough, a steam engine which develops torque at very low revs and can thus dispense with a gearbox.

2 comments:

Plutarch said...

Apart from the absence of gears, I heard someone say on TV that those Olympic bikes possess no brakes. So setting aside the problem of starting, what about that of stopping?

Barrett Bonden said...

This is true. However the back sprocket is fixed (ie, no free-wheel). To stop you merely stand on the pedals to stop them - and the rear wheel - from rotating.