Quotes of the day 11th February 2015
"It is not enough to have a good mind; the main thing is to use it well."
(Rene Descartes)
(Rene Descartes)
Nick Herbert on his visit to flood hit areas of Cumbria
Please note that the post below was published more than ten year ago on 21st November 2009 Nick Herbert MP, shadow cabinet member for the Environment, Food, and Rural Affairs, was in Cumbria this morning to see the areas affected by the flooding. He writes on Conservative Home about his visit. Here is an extract. I’ve been in Cumbria today to see the areas affected by the floods. I arrived early in Keswick where I met officials from the Environment Agency. Although the river levels had fallen considerably and homes were no longer flooded, the damage to homes had been done. And the water which had got into houses wasn’t just from the river – it was foul water which had risen from the drains. I talked to fire crews who were pumping flood water back into the river, and discovered that they were from Tyne & Wear and Lancashire. They had been called in at an hours’ notice and had been working on the scene ever since, staying at a local hotel. You cannot fail to be impressed by the...
Comments
Take a simple example like driving a car and stopping distance. Now we all know that the highway code gives the 30MPH braking distance as 14 metres (and we all know thats rubbish), it also gives the 60MPH distance as 55 metres (and we all know that's rubbish too, any episode of Top Gear will show you that). But there in lies the problem, the problem is not that the important point is wrong, the problem is the method of teaching is wrong.
Braking distance of a car depends on a a few things, given as d=V²/2μg where d is the distance, v is velocity (speed), μ is the braking co-efficient and g is gravity.
Now μ is very variable, its worked out by the mass of the car, the effectiveness of the brakes and the grip it has on the road. all may change (if it rains you have less grip, if there is a full load of passengers and luggage it has more mass, and if brake pads are badly worn then you have less efficient brakes)
However the important point is this, its not really a distance that can be measured in metres and then apply to every car (too many variables) but notice that the V² is always there. this means that on any given day in any given weather and with any given load, there is a quadratic relationship between the distance taken to stop and the speed of the car.
This means that if right now at 10MPH you can stop in exactly 1 foot then the following applies
10MPH - 1 metre
20MPH - 4 metres
30MPH - 9 metres
40MPH - 16 metres
50MPH - 25 metres
60MPH - 36 metres
70MPH - 49 metres
80MPH - 64 metres
you see, I guess what i am saying is instead of teaching given stopping distances in metres, so people then just think it's all tripe. Why not just teach the important point, that is if you double your speed you increase the distance in which any car can stop by a factor of 4, then we see we have good teaching, if you are doing half the speed you can stop in 1/4 of the distance.
Thats a law of physics, and well as a trekky friend in the RAF used to often say to me "Ya canna change the laws a physics Jim"
that's one example of the way a very valid lesson is taught en-mass in such an unapplicable manner, that poor thinking results. "Oh, the highway code states figures from some old British Leyland that does not apply today, or to me"
"If you have your speed you can stop in 1/4 of the distance"
Its also a fantastic type of law, there is no fine for breaking it as physics says it can not be broken, even if you are the Stig.
If you do manage to break it not only would you not get a fine, in fact you would probably get a nobel prize to go with your top gear trophy.
I have been told of an even better way to check whether you have left enough space between you and the vehicle in front than attempting to estimate a safe distance in metres (or yards), because the Mark one Eyeball does not come equipped with a digital readout giving you the exact distance in metres (or yards) to the car in front.
It's called the two-second rule and although it is not perfect - it does not take account of the quadratic relationship you correctly refer to between speed and stopping distance, for instance - it has the advantage that any adult of above bottom-decile intelligence can easily learn to count off two seconds in their head by methods such as mentally reciting at conversational speed "One thousand and ONE, one thousand and TWO."
What you do is watch as the vehicle ahead approaches some clear landmark such as a lamp-post, and from the instant it reaches the landmark, immediately count off two seconds. If by the end of that two second period your own vehicle has reached or passed the same landmark, you are too close at the current speed and should drop back.
Among other benefits this makes you more aware of how far a car can go even at 30 mph, never mind 70mph, in two seconds - which is quite frightening but good to be aware of.
you can add to it when its raining, "only a fool breaks the two second rules, but when it pours, the wise leave four"
:)