Thursday, 17 January 2013

How to slow down the Earth's speed of rotation.

A work colleague sent NSB a list of physical constants earlier today, amongst which was one which rather caught NSB's attention.

The property in question was the Earths "Equatorial Moment of Interia" and it got NSB thinking that, whilst the earth no doubt has a lot of inertia, whether there was some practical way of slowing it down a bit. Just for a laugh.

As NSB is somewhat mathematically challenged, the advice of a number of colleagues was sought during the lunchbreak, with the initial conversational gambit going something like this..

NSB (to colleague) : Can I ask you a technical question?

Colleague : Sure

NSB : If you had a large solid ball... say, perhaps, the size of the earth...

Colleague : Yeeess?

NSB : And suppose that it rotated at a particular speed... say, perhaps, once every 24hours...

Colleague (a bit nervously) : Mmmmm?

NSB : How could you work out how much force you needed to apply to slow it down?

Colleague (very gamely going with the flow) : Well, first you would need to know the Earths moment of Inertia.

NSB : Oh, I've got that number!

Colleague : How silly of me, what was I thinking. Of course you have that number just lying around your person. After all, who doesn't?

...and so on.

The colleague was very helpful, but what really made NSB's life easy was finding out that a contributor to New Scientist had already done all the maths.

Somewhat ambitiously, they had attempted to find out how long it would take the thrust of the Space Shuttle (lying flat at the equator and directing their thrust opposite to the earths direction of rotation) to slow the rotation of the Earth down to a complete stop.

And rather discouragingly, the result was 840billion years, or 60 times the age of the Universe. NSB imagines that it will be difficult to sustain enthusiasm for the project over such a long timescale, and fuelling the rocket motors for that length of time would also be a significant technical challenge.

So NSB decided to take a much more practical and pragmatic approach by using a more easily fuelled power source (jet engines) and a more realistic target (slowing the length of a day by 0.1 seconds).

Of course, one jet engine really isn't going to make much of a difference, so it might be necessary to requisitiion all of the worlds finest Rolls Royce aero-engines in service today (NSB has no doubt that airlines could be persuaded to donate their engines by the potential PR benefits of being associated with such a world-changing project.

And one would need to site all the engines on the Equator for maximum effect, which would provide a significant engineering benefit for the (often developing) countries concerned.

Another approach might be to simply fly the relevant planes to airstipes on the equator, tie the planes down, and run the engines whilst still attached to the planes.

Anyway, leaving aside these small technical details, NSB crunched through the numbers and came to the result that, woth all of Rolls-Royces installed base aero-engines (some 400million lbs of thrust) operating round the clock, it would take around 24,000 years to slow the earth down such that the day was 0.1 second longer than it is currently.

Which still seems rather a long time.

Realistically, NSB suspects that the airlines will want their engines (or planes) back before the project has achieved its aims.

And NSB can't think of a practical way of achieving the desired aim in a shorter period of time.

So, dear reader, do you have any suggestions of ways to slow the earth down more quickly?

Hello, Can we plesae borrow your engines for 24,000 years?

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