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The All New Groundspeak Uk Pub Quiz!

The Golem
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The Golem

+The Golem

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Posted

Is it the other end of the giants causeway of the coast of scotland, photo taken from the mouth of fingals cave on the isle of Staffa? (Amazing what you learn on "coast")

 

Ping!

 

The Nutters are correct - here's an email I received from them:

 

"I think I may of got the answer to your question correct but will be away this weekend, if it is right would you set this question on my behalf please, (the bummer is you won't be able to answer it :))

 

Frenchman Jean Blanchard made the first crossing of the English Channel by what in 1785?"

 

Very organised!! :)

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The Forester

+The Forester

Posted
Posted

Albert Einstein had an idea or two about Relativity. Basically, fings wot go fast have funny effects.

 

My question is a multipart one. What effects does Relativity have on our GPSs, if any?

 

Think of Alberts' analogy of the squishing/stretching effects of a Viennese tram at speed.

 

The satellites are whizzing around at tremendous speed and have extremely accurate clocks onboard, so the effects, if any, are easily measured.

 

i) Does General Relativity speed up or slow down the GPS signal? ie, does the indicated range from the satellite increase? or decrease? Extra points for saying by how much, if any.

 

ii) Does Special Relativity speed up or slow down the GPS signal? ie, does the indicated range from the satellite increase? or decrease? Extra points for saying by how much, if any.

 

iii) Do the two Relativisitic effects affect the signal in the same sense? Or in opposite senses? Or not at all?

 

iv) If Relativity materially affects the accuracy of a geocacher's GPS fix, how does/would/could the GPS compensate, if at all?

 

Usual rules apply. Conferring is allowed, but not referring - such as to old school textbooks or the innernet. Judge's judgement will be pig-headed and perhaps wrong, but open, honest, final, and questionable.

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sTeamTraen

+sTeamTraen

Posted
Posted

OK, here goes, at the risk of making a total pillock of myself (not least in front of my son who is currently studying this in physics), and 28 years after I studied any of this:

 

i) The satellite's clock seems to be running faster than mine, so that means that, er, it's counting faster, so I think that means it appears to be further away than it is.

 

ii) At any given time any given satellite can be moving either towards or away from you, so on average I would say it cancels itself out.

 

iii) If ii) is right then the answer is "it depends"

 

iv) I suspect that any Special Relativity effect is negligible, and the General Relativity effect is roughly constant and therefore discounted by the software.

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The Forester

+The Forester

Posted
Posted

sTeamTraen's answer is brilliant, erudite, wrong, and quite confused.

 

Pure Eurocratese, in fact.

 

iii) If ii) is right then the answer is "it depends"
deserves to be framed and put up on a wall.

 

So far, sTeamTraen wins the coconut, though for entirely commendable and entirely wrong reasons.

 

At any given time any given satellite can be moving either towards or away from you
deserves a seat in the Cabinet on the Foreign Office side of the fence.
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sTeamTraen

+sTeamTraen

Posted
Posted

sTeamTraen's answer is brilliant, erudite, wrong, and quite confused.

 

Pure Eurocratese, in fact.

 

iii) If ii) is right then the answer is "it depends"
deserves to be framed and put up on a wall.

 

So far, sTeamTraen wins the coconut, though for entirely commendable and entirely wrong reasons.

 

At any given time any given satellite can be moving either towards or away from you
deserves a seat in the Cabinet on the Foreign Office side of the fence.

 

Oi! Unfair!

 

I'm prepared to discover that my answers to i) and ii) are a load of dingo's kidneys. But if they are both right then iii) follows logically. Not Eurocratese but logic. (If only we had more logic here...)

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Kitty Hawk

+Kitty Hawk

Posted
Posted

I've just spent most of Jonathan Ross's interview with the Farrell man and the contents of my 4th JD & coke thinking this over.

 

My conclusions:

 

i) depends if you are east or west of the satellite as to whether it is nearer or further, but there would be a slight shift to the east, by the distance that the eath rotates in the time it takes for light to travel from the stellite to the earth.

 

ii) hmmm, does gravity speed up the signal - I think not so No.

 

iii) No

 

iv) The distance is too small to worry

 

Ross isn't on form tonight.

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Simply Paul

+Simply Paul

Posted
Posted (edited)

i) Does General Relativity speed up or slow down the GPS signal? ie, does the indicated range from the satellite increase? or decrease? Extra points for saying by how much, if any.

 

As the GPS signal is a radio-frequency electromagnetic radiation, it's fixed at 186,282.3970 miles per second: The speed of light. The motion of the transmitter and/or receiver can affect the observed wavelength, but not the speed of the signal. As the satellite approaches us it is actually anything up to 20ish metres ahead of where it 'seems' to be, and as it receeds from us, it's further away.

 

ii) Does Special Relativity speed up or slow down the GPS signal? ie, does the indicated range from the satellite increase? or decrease? Extra points for saying by how much, if any.

 

Again, the signal's speed is unchanged. However, as the satellite is 'experiencing' time slower than we are because of relativistic motion, the wavelength of the signal is lengthened and the frequency dropped.

 

iii) Do the two Relativisitic effects affect the signal in the same sense? Or in opposite senses? Or not at all?

 

I think the two theories say different things, but cause similar 'red/ blue shift' effects on observed wavelength and frequency. The speed of the signal, which is always referenced above, remains unchanged though.

 

iv) If Relativity materially affects the accuracy of a geocacher's GPS fix, how does/would/could the GPS compensate, if at all?

 

If there's a fixed frequency the satellite uses, how far from it the 'ground station' receives the signal will let the GPS adjust for Doppler Shift and the relative motion of the transmitter.

 

If I'm close enough for a ding, ping or dong... Pub quiz! Which company is the world's largest tyre manufacturer, based on units sold?

Edited by Simply Paul
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Team Maddie UK

+Team Maddie UK

Posted
Posted

A hard one to get the head around this one.

 

i. The 'speed of the signal' however, is fixed at the speed of light and doesn't vary under any circumstances (this being the major tenet of the theory itself). General Relativity as I recall would suggest that a clock further away from the Earths centre of mass would run faster. That would result in a steadily increasing error in the time difference measured by the receiver. The receiver would have to come to the conclusion that the signal was sent from some time in the future and therefore took a negative amount of time to reach it resulting in a negative distance. (This is getting very confusing so I'm going to stop before my brain explodes).

 

As to the magnitude of the error and the extra points... well you can <insert expletive> right awf! I can't now remember the formulae for calculating this sort of thing as it's now 35 years since I studied Physics at Uni and haven't had cause to use them since. (until now that is :laughing: Further to this, I seriously doubt that, even with a calculator at my disposal and the formulae ready in my head, I would be able to put the two together in a meanigful manner after a few pints in a pub!

 

ii. 'Speed of the signal'? again see above. Special Relativity is all about the relative speed of the craft to the observer (GPSr in this case). The faster you go the slower your clock goes and you stay much younger than the poor geocacher on the ground hunting his tupperware. This is essentially the opposite effect of the above and would result in a steadily increasing error in a positive sense; the sattelite appearing to be further and further away than it really is. (not nearly as confusing and my brain has now averted a total melt-down)

 

As to the magnitude of the error and the extra points... see (i) above.

 

iii. As stated above they effect the result in opposite senses.

 

iv. This is an interesting one. Since I had never considered this problem before I have to assume that either the resulting errors are too small to be considered significant or that some form of compensation is actually being performed. The former seems unlikely as even if the difference in clock speed was very small it would be cumulative and eventually become significant at some time in the future. So how is it sorted out? Perhaps the US military can uplink to the satelites periodically and reset the clocks? Or, since the effects can be calculated the clocks could be adjusted in some way so that they would be incorrect on the ground but, once in orbit, would run at the correct speed. It would still seem to me however, that the margin of error in terms of the orbit etc. would still require some form of periodic adjustment.

 

This is probably all bollox and my brain will have to explode anyway when I read the Foresters inevitably long and detailed correct explanation once everyone has had a crack at this.

 

Martin

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The Bongtwashes

+The Bongtwashes

Posted
Posted

As with Team Maddie UK, it's decades since I studied this, so any calculations would be strewn with errors, but basically I agree with TMUK.

 

i. General Relativity: The nearer an object to a large mass (eg the Earth), the slower time passes, therefore time runs faster for the satellite than the receiver.

 

ii. Special Relativity: The faster an object is travelling, the slower time passes, therefore time runs slower for the satellite than the receiver. I tried this calculation, and came up with over 0.25 seconds per day, which I'm sure is several orders of magnitude too high.

 

iii. As stated in i. and ii. above, they have opposite, almost certainly non-equal, effects.

 

iv. To compensate, every satellite is 'corrected' regularly (not sure, but I think it is daily). and the base frequency of the clock on the satellites is tweaked before launch, so that if the satellites were stationary, their clock would run at the wrong rate.

 

v. My brain hurts too!

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The Forester

+The Forester

Posted
Posted

I'm going to give Pimply Saul a dong, but it might sound like a ding 'cos Viennese trams at speed do that to dings & dongs.

 

Honorable mentions to all the other answerers too.

 

Starting with the last question first: the satellites clocks are tweaked before launch to compensate for the combined effects of Special and General relativity. Second generation satellites also make further much smaller adjustments on the fly. Thirdly, our own humble GPSrs also take Reletaivistic effects into account when processing the satellite data

 

Qiii has been well answered. Yes, Special and General are of opposite sign, though vastly diferent magnitude.

 

Qs i & ii were to get the neurons ticking over and to prep you for Q iii.

 

Excellent answers all round. Talking of which, I'm on the bell.

 

Dang!

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Archer4

+Archer4

Posted
Posted

Yeah, had a check after I answered as I'd heard they were outsourcing production. Seems that hasn't kicked in yet.

 

Bit short of inspiration, brain all coded out, so for what is the name "LEGO" derived?

 

BTW, there's a correct answer and a co-incidental myth.

 

It's the name of the inventor or inventors - can't remember what without looking it up but was it someithing like LEif GOrenson :laughing:

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Archer4

+Archer4

Posted
Posted

Yeah, had a check after I answered as I'd heard they were outsourcing production. Seems that hasn't kicked in yet.

 

Bit short of inspiration, brain all coded out, so for what is the name "LEGO" derived?

 

BTW, there's a correct answer and a co-incidental myth.

 

It's the name of the inventor or inventors - can't remember what without looking it up but was it someithing like LEif GOrenson :laughing:

 

Clang

 

Oh no it isn't :blink:

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slimey

+slimey

Posted
Posted

What is the first term in the following series?

 

?,11,17,23,35,53,83,131,305,.....

 

(HUGE apologies if I've done any typos in that line)

 

Hmmm.... I can't make 305 fit, but there's an obvious pattern in the rest of the numbers, which I think would make the first number 11. If that's the right answer, I'd expect it to be 209 then 335, instead of 305

 

Of course, I'm probably totally wrong :blink:

 

Simon

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