And the Physicus winners are…

It's been a busy week at Reg Merchandising. Our Physicus competition attracted 601 entries, so many that publisher Tivola kindly agreed to offer another five copies.

So, we now have 10 happy punters who correctly answered the question: "What is the value of the gravitational constant?" Meaning big G, not little g.

And the Physicus winners are:

C. Conover
Larry G. Felix
Lew Foti
Chris Gillings
Charles Hodson
Matt Piechota
Bruce Taylor
Bob Williams
And two chaps known only as Brett and Chris

Well done to you, and thanks to everyone who entered.

But shame on those of you who came up with the figure 9.81m/s/s. This is the value of the acceleration due to gravity (on Planet Earth, etc. etc.)Blimey, even I knew that and I'm just the office cleaner.

The answer is - more or less - 6.664x10-11 N.m2-kg-2. Right, before you all start moaning, I know that this is up for debate.

That's why we did not demand the exact figure written on the post-it-note fixed to my mop bucket.

Lucy Sherriff, our resident boffin, has appended a note on this fascinating controversy.

OK - the Gravitational constant Lucy writes. Not a theoretically determined value, and therefore not set in stone. It's also a really tricky one to pin down.

The first person to have a proper go at it was Cavendish, who managed to measure G in his famous experiment with a torsion balance about 200 years ago. This is often referred to as "weighing the earth".

G is so difficult to measure because gravity is such a weak force, and measurements require extremely sensitive equipment. One way to think about it is this: The total gravitational force twisting the pendulum of a typical Cavendish torsion balance is equivalent to the weight of a bacterium, and this force must be measured extremely accurately.

Irritatingly, as more results from experiments like Cavendish's come in, the uncertainty surrounding the value seems to increase. However, despite this, it is generally accepted to quote it to three significant figures. ®