Yearly Archives: 2011

Why 80mph is not a good idea

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The UK government has announced that it is beginning a consultation on raising the speed limit on UK motorways from 70 mph to 80 mph. I don’t think this is a very good idea, and my reasons are listed below.

Time Saving

You simply don’t save that much time by increasing your speed to 80 mph. If you drove the 400 mile distance from London to Edinburgh, you would only save three-quarters of an hour, and that assumes that you maintain a constant speed of 80 mph the entire time, neither accelerating or decellerating.

Assuming no acceleration or deceleration is entirely unrealistic and as it takes longer to accelerate to 80 mph than it does to get to 70 mph, the graphs above represent a best case scenario. The real time savings are likely to be much lower.

Kinetic Energy and Stopping Distance

Kinetic energy at different speeds for my car, a Peugeot 207 with a mass just over 1000 kg.

The kinetic energy of a vehicle is what makes it dangerous; transferring that kinetic energy to an object – be it a pedestrian or another car – is what causes damage. Kinetic energy depends on the square of the speed; if you double the speed of an object you quadruple its kinetic energy. An increase in speed from 70 mph to 80 mph is a 14% increase in speed but this results in a 31% increase in kinetic energy, making the car – in a sense – 31% more dangerous to other road users.

Increasing kinetic energy also increases stopping distance. Increasing the speed limit to 80 mph would increase the average stopping distance on motorways to 120 metres (30 car lengths!), a 25% increase on the 96 metre stopping distance found at 70 mph.

Fuel Economy

The relationship between speed and fuel economy is not linear; fuel economy is poor at both low and high speeds and peaks somewhere between 40 and 60 mph. Driving at 80 mph will decrease fuel economy and therefore increase fuel consumption; fuel costs will be higher and CO2 (and other harmful gas) output will be higher. Our limited supply of petrol will be depleted faster if we all drive at 80 mph than if we drive at 70 mph.

SkySails

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On July 7th the German company SkySails GmbH was awarded the Sustainable Shipping Environmental Technology of the Year Award (for the second time) for its SkySail technology.

The SkySails system uses a computer controlled kite with an area of more than 160 square metres to harness the power of wind as an auxilliary power system for large marine vessels. The SkySails company claims it can reduce fuel consumption over long journeys by between ten and fifteen percent.

The SkySails system is a form of high altitude wind power (HAWP). HAWP systems are viable because the power available to wind power systems increases with the cube of the wind’s speed (e.g. if you double the speed the energy produced increases by a factor of eight) and wind speed increases rapidly with height. Companies like KiteGen are even working on using HAWP systems for electricity generation.

Lactose tolerance

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Because most in the western world are able to digest dairy products it is often assumed that this condition (lactose persistence) is the norm. But if you are able to tolerate lactose then you are actually in a minority: ninety-eight percent of Southeast Asians and ninety-five percent of Chinese are lactose intolerant. Between them these two ethnic groups make up more than 28% of the world’s population.

The graph below shows some of the ethnic groups with over 50% of the population lactose intolerant:

 

Liquid cooling

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Computer hardware produces a huge amount of heat when operating. Usually this heat is removed by a combination of heatsinks and fans

The grey heatsink conducts the heat away from the processor and the sink’s fins give the heatsink a larger surface area for the air moved by the fan to blow over. Some computers use very large heatsinks in order to do away with the need for a fan entirely, relying only on natural convection currents for cooling.

Some computers do away with fans by pumping water past the heatsink; water is a much better absorber of heat than air* and therefore the system uses less power for cooling.

Green Revolution Cooling have gone one step further – they actually submerge the computing hardware in a special non-conductive liquid. This liquid then circulates, transferring the heat away to an external evaporation tower.

They claim that their cooling system will pay for itself within 1-3 years.

* The specific heat capacity of air is 1.007 joules per gram per kelvin and the specific heat capacity of water is 4.187 J/g/K. This means that water will absorb more than four times the energy of the same amount of air for the same increase in temperature. Green Revolution don’t say what the specific heat capacity of the fluid they use is, but it’s likely to be greater than water’s.

Hacking PIN pads using thermal vision

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There is a mission in the first Splinter Cell computer game where you have to use your thermal vision to read a keypad code entered by a guard. Researchers from University of California San Diego have now shown that this is entirely possible.

Building on earlier work by Mike Zalewski the researchers have shown that codes can be easily discerned from quite a distance (at least seven metres away) and image-analysis software can automatically find the correct code in more than half of cases even one minute after the code has been entered. This figure rose to more than eighty percent if the thermal camera was used immediately after the code was entered.

K. Mowery, S. Meiklejohn, and S. Savage. 2011. “Heat of the Moment: Characterizing the Efficacy of Thermal-Camera Based Attacks”. Proceedings of WOOT 2011. (.PDF 9.53Mb).