Kinetic Energy?

Speeding is not cool!  – “How Science Works”


Shadow Chancellor Ed Balls has confessed to being caught speeding, saying he was “bang to rights”.

The Labour MP said he was going at 56mph in a 50mph zone on the motorway in his West Yorkshire constituency.

Writing on his blog, he said he had paid a fine and attended a speed awareness course rather than accept penalty points.

Mr Balls was caught by the police using his mobile phone while driving during the 2010 general election campaign.

It was reported at the time that he had been fined £60 and given three points on his licence, but a spokesman for Mr Balls said police returned his cheque and the points were never applied, meaning he has a clean licence.

The Morley and Outwood MP attempted to laugh off his latest motoring offence, saying he had been going “too far, too fast” – one of his favourite attack lines against the coalition’s budget cuts.

“Like many local people, I was caught out by the never-ending roadworks on the M62,” said Mr Balls.

“Pulling on to the motorway at Morley, I realised too late that the speed restrictions were still in place.

“I was caught and bang to rights – doing 56 in a 50 mile restriction zone.

“Going too far, too fast, you might say.

“I paid my fine and chose to attend a speed awareness course. I currently have no points on my licence and would like to keep it that way.”

Describing his speed awareness course, he added: “I ended up in the Holiday Inn with 39 others.

“The course was very professional and actually really worthwhile.”

‘Fair cop’

Mr Balls said the experience had made him even more determined to get 20mph zones on busy roads in the area.

“What hit home were the statistics which link speed to car deaths. At 20mph, less than 10% of people will lose their lives if hit by a car.

“But the probability rises exponentially, going above 40% at 40mph.”

Science behind this….

Well in fact Ed and the course are right of course, this is very good Science also well done to the BBC and their Science reporting.

If we think about the energy contained in the motion of a car which is travelling at 40 mph instead of 20mph. Since kinetic energy is related to mass and velocity by a more complex equation of KE = 0.5mv2 we find that if we double the speed the energy contained in a car is x4.

This means that of course a speed double is in fact x4 as dangerous in terms of the energy which is required to be lost on impact.

Hence, if you are hit by a car travelling twice as fast there is a much greater risk of death!

However, I would add that Ed was only going 6 mph over a 50 limit so the energy increase would be much smaller than this, also the chances of being run over on this part of the road is small as it is a Motorway, so keep things in context!

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  1. I think the problem with this argument is that the logical conclusion is to reduce the speed limit to zero. Clearly this is absurd, so society has to make a judgement on the balance between the utility on the one hand versus the risk on the other.

    There is no right balance. Some people may think the 50mph limit on a stretch of road is too high; others might think it about right; others might think it too low. None of them are right, none of them are wrong.

    Do you remember that advert on the TV a few years ago? It explained how many children are killed when hit by a car at 40mph. It then said (something like) “At 30mph, 4 out of 5 children survive an impact with a car.” Thus the mesage is: don’t exceed the 30 limit. But, one might equally say: “1 in 5 children are killed at 30mph! That’s dreadful!! We must reduce the speed limit to 20mph immediately to avoid this carnage.” Or perhaps that should be 10mph? Why not? Why not a man with a red flag?

    For me, this is one of the biggest problems with the speed limits: they are essentially arbitrary. Unlike murder, theft, assault, etc, there is no logical or moral basis for determining a particular speed limit. It’s just a matter of opinion, and I think that is why a lot of people regard breaking the speed limit as morally different from going out and mugging someone. It *is* morally different. There is no “morally correct” speed limit.

    For what it’s worth, I think the standard 30mph limit is far too high in a lot of modern housing estates with narrow, winding roads, and I think it’s too low on a number of other roads (in Nottingham, between Basford and Arnold, we have a full-width dual carriageway with very wide verges and excellent visibility, but it has a 30mph limit enforced by cameras; it seems ridiculously low when driving along it).

    Although the science (“KE = 0.5 m v squared”) is of interest, it cannot in this instance give us the “right” answer, unless you accept zero as right.

    1. Steve,

      As you say zero is the only way!


      Animated Admin

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