Monday, 27 January 2014



I call this 'The Stiff String Theory' because it has to have a name
(Or how you can  reach Light Speed in space with a big watch)

Please can you answer this simple mathematical conumdrum for me:


Imagine a turning watch hand of gigantic proportions somewhere out in space where there is no RESISTANCE
(or an imaginary laser of fixed length or long piece of stiff string)
(Impossible I know - but use your imagination ! )


Say it is 10 miles long


Fixed at one end to a central pivot 

The hand / laser/ stiff string starts to turn like a big clock hand

OK up to now?
(Hope you can imagine that)


Turning at say 1 Revolution Per Minute

The free 'end' will travel 1 entire circumference of the 'Turn' in the same time as a point along the 'Stiff String'  just 1 metre from the pivoted end , but it will travel much further in doing so and, importantly, at much higher speed:

THE QUESTION IS: How long would the imaginary hand / laser / Stiff String' have to be for the free end to theoretically be travelling at the speed of light? (299,792,458 m/s)


I think as an example;

The point along the 'Stiff String' that is 1 metre out from the pivot,  traverses a  circumference of 3.14metres at the speed of 3.14m per minute,  or .052333 m/sec


While the free end will rotate in the same time (1 minute) but covering a distance of 31.14 miles  in 1 minute, or 921.5 m/sec


(Working with Pi, on Speed = Distance travelled / Time taken etc I assume it should be possible to calculate the length of the pointer the end of which, at 1 R.P.M,  reaches theoretical light speed ( but my calculator runs out of zeros! )

 I assume turning the pointer at higher R.P.M (Say 20,000 R.P.M) would reduce the length of pointer required to reach light speed by 20,000?

It's beyond me but I feel I need to know the answer (If you ask 'Why?' I would probably answer  'Because it's there' -But then it's not 'There', it's actually in my imagination!)

(I do actually like working with big numbers but my calculator doesn't)

So, if you can work it out and leave the answer in a comment here - I would be very grateful to you

Egal Bohen


Anonymous said...

speed = distance / time

distance = circumference = 2 * Pi * radius
time = time_per_revolution
speed = speed_of_light

speed_of_light = 2 * Pi * radius / time_per_revolution
radius = speed_of_light * time_per_revolution / ( 2 * Pi )

speed_of_light = 300 Million meters per second
time_per_revolution = 60 seconds

radius = 2.86 Million Kilometers

Egal Bohen said...

Thanks Anonymous

Not sure if I can get a piece of stiff string that long.

Will have to spin it faster!