On...The Lincolnshire Earthquake (or, a little knowledge can be a disturbing thing when you are half-asleep)

At four minutes to one GMT this morning (27th Feb 2008) I was having an interesting dream about flying in an RAF fighter jet. The take-off had been particularly hairy with the pilot nearly clipping trees and buildings and then pulling some interesting low level manoeuvres. I never found out how the dream ended though as I was awoken by the house shaking. It seemed as though a large fleet of heavy-goods vehicles were driving past about a metre from my bedroom wall in an East-West direction. Now sufficiently awake to remember that my bedroom wall is in fact nowhere near a major road and the shaking was of a different nature to anything produced by lorries I concluded that it must, therefore, be an earthquake. My wife told me I had said it was an earthquake and got to the window before the shaking stopped. As the quake only lasted about ten seconds, brain and body must have been in overdrive.

Now you just don't get earthquakes in Lincolnshire. My sleepy brain continued racing. We are nowhere near a tectonic plate boundary, I remembered, and earthquakes in the middle of plates can be severe. However the shaking had quickly stopped and, although alarming, little damage appeared to have been done. But then from the recesses of my mind I recalled (how accurately I don't know without checking) from an oceanography course I had done that off the coast of Norway there is a large unstable undersea slope which could slump if disturbed by an earthquake, displacing a vast quantity of water and inundating the east coast of Britain.

In a sleepy state we seem to be more prone to projecting our fears onto situations, possibly because of an ancient threat-assessment mechanism evolved to wake us up quickly, analyse the situation and plan action if danger threatens. I spoke to my mother this morning and she said she awoke thinking there was a burglar in her house. I had imagined a tsunami. Fortunately both fears turned out to be unfounded and if we had been awake when the quake occurred we probably would have had different thought processes.

[BBC Breakfast News said the earthquake had a magnitude of 5.2. BBC Look North contradicted them and said it was 5.3, but then they may have just been a little excited at having a national news story happening on their doorstep.]

On... The Cycling Null Point

When cycling one constant is the movement of air.

You are moving through the air as you move over the ground and the air that surrounds you is probably moving too, as a breeze or wind (which if strong almost always seems to be a head-wind rather than a tail-wind for some reason). The relative movements of you and the air mass you are cycling through can sometimes make progress hard work but most of the time the movements are more subtle. You can hear a fairly light breeze as it moves past your ears, your eyes and nose can feel small air movements and your lips more sensitive still (especially if you wet them).

However, just occasionally, it is possible to experience a 'null point' where your movement through the air exactly matches the movement of the air surrounding you relative to the ground. At the null point you are moving but are in (it seems to you) completely still air, and not a trace of breeze can be felt. The sensation is strange and, despite cycling most days, is one that I have very rarely experienced and never for more than for a few seconds.

For a null point to occur, the movement of the wind must exactly match your speed and direction on the cycle, at least within your ability to detect any air movement caused by the difference. Experiments carried out in a closed room show that the face is capable of detecting air movements of less than 10cm per second but as the distractions of the road are likely to reduce sensitivity I will use this figure.

Next I will assume a fairly sedate average cycling speed of 20 kph (about 12.5 miles per hour). 20kph is about 5.5 metres per second. As a wind of 0.1 metres per second is detectable the moving air must be within the range 5.4 to 5.6 metres per second. It must also be blowing directly from behind otherwise there will be some movement across the face which will be detected – I would estimate that a wind within say 10 degrees of directly behind is undetectable.

Lastly, the wind (if there is one, remember absolutely still air will seem like a 20kph breeze on the bicycle) will have to be moving in a uniform direction and not swirling. When air is moving there is, however, usually some swirling or gusting but it is difficult to put a figure on how common this is. Suffice it to say a mass of air moving in a uniform direction and speed without any swirling or gusting for more than a few seconds is unusual. Of those winds that do, only a small percentage of will be in the 'right' direction and only a small fraction of those will be blowing at the 'right' speed. Which explains why the null point is unusual. So if you should happen to experience one then enjoy it while it lasts.