Paul Dundon’s Weblog

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A little cheese and a little whine

The physics of transport – in commonsense figures

One of the things often forgotten in the debate about transport is how convenient the petrol-driven car is as a mode of transport. Not only is the car available at any time of day, and available to start your journey whenever you want, but it can take you all the way to your destination. Even in built-up areas, in 15 minutes – about the time it takes to have a cup of tea – you can reach any destination in a 6 mile radius, an area of 32,533 football pitches. For long distance travel, the motorway network means that in the same time (1 tea-break) you can easily travel almost 20 miles or the length of 3,839 double-decker buses.

Then there is the performance of the engine. Even quite ordinary cars are now capable of speeds and accelerations which one hundred years (or 3.5 million tea-breaks) ago would have been unthinkable. Our household hatchback, for instance, has a top speed of 5,279 double-deckers / tea-break, and can reach around 3,000 double-deckers / tea-break in just 1/60th of a tea-break – an acceleration of almost 175 kilo-double-deckers / tea-break2.

This is no small feat. The average car weighs in at about 1400kg – the weight of 0.23 elephants. That means the acceleration we just talked about needs 10,455 elephant-football pitches / tea-break2 of energy. To put that in context, a McDonald’s milkshake contains 37 kilo-elephant-football pitches / tea-break2. In other words, getting a car of average weight up to speed can use around 0.28 milkshakes of energy. The total amount of energy required for even a short journey is clearly orders of magnitude higher.

Once at speed, the energy requirements drop considerably, but the rate at which energy has to be delivered is still significant. Keeping a car moving in traffic at about 5,700 double-deckers / tea-break requires about 10 milkshakes / tea-break, or 368 kilo-elephant-football pitches / tea-break3. And that’s a lot of hard work for any sort of battery.

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Filed under: Humour

One Response

  1. Keith says:

    It’s all so much clearer now.

    However, your initial statement that you can get anywhere in a 6-mile radius in 15 minutes assumes that there are no other cars, double-deckers, elephants, or workers on a tea-break on the roads at the same time.

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My Bookshelf

The Golden Bough
The Value of Nothing
The Fire
A Wolf at the Table
Devil Bones

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