# Series K- Kinetics

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 1032784.  Sat Nov 02, 2013 6:24 am On this episode they talked about what would happen if the Earth suddenly stopped spinning. Other than colliding into things and one half of the planet being in total darkness while the other is in perpetual light, what are the other effects. Could life survive if the Earth stopped spinning?

 1032791.  Sat Nov 02, 2013 6:53 am

 1032817.  Sat Nov 02, 2013 10:56 am Was anybody else thinking of the episode of Futurama where the Earth stops spinning? Because in essence just saying what happens there would be the correct answer.

 1032828.  Sat Nov 02, 2013 12:07 pm Part of the problem is which part of the earth do you try to stop? If you hang on to part of the crust, then you'd rip it open like the skin on a custard and make a gigantic new super volcano and mountain range. If you hang on to all the crust, then the centre would (probably) still be spinning and would start everything spinning again when released albeit less spinny. Not to forget all the seas sloshing around. I wonder what effect it would have on the moon. How much heavier would I weigh (ignoring the excess cake eaten through worry)?

 1032849.  Sat Nov 02, 2013 3:15 pm If the world should stop revolvin' spinning slowly down to die, I'd spend the end with you and, when the world was through, then one by one the stars would all go out; then you and I would simply fly away. I thought this was the best of the 30 minute shows so far.

 1032850.  Sat Nov 02, 2013 3:32 pm We had an attempt at answering the question here: http://old.qi.com/talk/viewtopic.php?t=26439&start=0

 1033025.  Mon Nov 04, 2013 3:39 am Yes, CB27, that was the inspiration behind the question. That, and some calculations done by Dr. Bob.

 1033035.  Mon Nov 04, 2013 6:23 am Surely the only things you need to know is how fast the Earth is spinning (1,000 mph at he equator) and the escape velocity* (25,000 mph). If we assumed the Earth just stopped dead and you kept on going, you would only be travelling at 1,000mph and so would be nowhere near escape velocity. However, the Earth is travelling around the Sun at about 67,000 mph. If that suddenly and mysteriously ceased, and you kept going than you would fly off into space because your speed relative to the Earth would exceed esacpe velocity. *"Escape velocity" should really be called "escape speed" because velocity is a vector quantity.

1033041.  Mon Nov 04, 2013 7:05 am

 Ian Dunn wrote: Other than colliding into things and one half of the planet being in total darkness while the other is in perpetual light, what are the other effects.

Neither half of the planet would be in total darkness or perpetual light. For that to happen, the Earth would have to still be rotating, at the rate of roughly one rotation every 365 days.

If the Earth stopped rotating, then a day would last as long as a year, but there would still be day and night.

 Posital wrote: I wonder what effect it would have on the moon.

Apart from not accelerating it away from the Earth anymore, not very much I'd imagine.

 djgordy wrote: Surely the only things you need to know is how fast the Earth is spinning (1,000 mph at he equator) and the escape velocity* (25,000 mph).

You seem to be implying that, if you're travelling any less than the escape velocity, you'll never leave the surface of the Earth.

This is clearly not true. If I jump into the air, I temporarily leave the surface of the Earth without ever getting close to escape velocity.

 1033053.  Mon Nov 04, 2013 8:40 am Did anyone note down the numbers mentioned to work out the size of His Fryness' mighty chopper? :)

1033054.  Mon Nov 04, 2013 8:54 am

 CB27 wrote: Did anyone note down the numbers mentioned to work out the size of His Fryness' mighty chopper?

Yes I did (I have to, listing all the facts mentioned for the British Comedy Guide).

Stephen is 6ft, 4.5in tall and weighs just over 14 stone. If Stephen were 44,000 miles tall his penis would be 3,384 miles long. Using that you can probably calculate his real penis length, but I'm hopeless at imperial measurements.

1033062.  Mon Nov 04, 2013 9:59 am

Re snails - it was in the E series episode 3 - Eating.

 Quote: Stephen Indeedy. So, the mongongo nut is collected from piles of elephant droppings, which, er, brings us all shuffling downstairs in our pyjamas to the ill-stocked refrigerator that is General Ignorance, so fingers on buzzers, please. What were the first animals to be herded for food? Jimmy [presses buzzer, which sings, "Food, glorious food!"] Stephen Yes, Jimmy. Jimmy Well, the first ones would have been experiments, so it would have been guinea pigs. Stephen Ah-h. Very good, very good, very good! Jimmy [snaps and winks] Alan Goats. Stephen Not goats. Phill [presses buzzer, which sings, "TV dinners!"] Stephen Yes. Phill Chickens. Stephen Ooh! No, not chickens. [Forfeit: Klaxons sound. Viewscreens flash the word "CHICKENS".] Stephen Chickens . . . Johnny [presses buzzer, which sings, "Spam Spam Spam Spam!"] Phill Oh, I've done it again! With the letters. Stephen Yes, Johnny. Johnny T-Rexes. Stephen Oh! Johnny Pterodactyls! Stephen No. Jimmy Godzilla. Stephen [sighs] If I tell you the Latin name-- Jimmy Was it . . . Oh, the Greeks! Johnny EGGS! EGGS! EGGS! They were easy to move 'round the field! [mimes rolling eggs around] Stephen [laughs] No . . . Johnny You could be a very lazy shepherd. Stephen Shall I tell you the Latin name? Would that help? Helix helix. Jimmy Helix helix. Ah. Stephen They've got a spiral on them . . . Audience in General [starts murmuring "snails"] Stephen So the audience knows . . . Alan Snails. Johnny Snails! Stephen Thank you, audience, for telling Alan. Alan [flashes a happy thumbs up at the audience] Jimmy They herded snails? That must have taken ages! Stephen You'd think! Absolutely. Alan [holds up one finger to the audience, points to himself, and mouths "one point!"] Johnny All they had to do was build a wall. Stephen Snail farming seems to date back to 10,700 B.C. The earliest things archaeologists have ever found that we appeared to farm.

1033064.  Mon Nov 04, 2013 10:01 am

dr.bob wrote:
 djgordy wrote: Surely the only things you need to know is how fast the Earth is spinning (1,000 mph at he equator) and the escape velocity* (25,000 mph).

You seem to be implying that, if you're travelling any less than the escape velocity, you'll never leave the surface of the Earth.

This is clearly not true. If I jump into the air, I temporarily leave the surface of the Earth without ever getting close to escape velocity.

Well I suppose DJG's sort of right, although he's missed a couple of steps in the explanation and is being confused by trying to relate it to "escape velocity" when that's actually unrelated.

Consider object A (a human by the curious name of "Dentar Thurdent") standing "stationary" in the carpark of Object B (his local Surrey supermarket [other planetary surface features are available]), approximately 100m to the east of the solid wall of the supermarket's in-store bakery. Assume this bakery was constructed very strongly, and with specific focus on resisting horizontal shock loads.

Now if the Earth (topsoil, crust, mantle, core etc - the whole mish-mash of "natural dirt, rock and subsurface stuff") suddenly stopped rotating, but Dentar Thurdent didn't. Dentar would continue with his existing tangental velocity at an initial speed of around 640mph (Surrey not being at the equator). He would also contunue to be attracted to the centre of the earth at roughly 1g (9.81m/sec^2) and this weight would keep him glued to the surface of the planet UNLESS his orbital velocity is such that:

v^2/r > 9.81m/sec^2

(where "r" is the radius of the earth - call it 6,400km)

It isn't - in fact it's not even vaguely close, the answer coming out at around 1/750th of the value required to leave the surface of the planet purely by virtue of its curvature. But then we knew this anyway, because this would be true even *before* the earth stopped rotating (in fact the cesasation of rotation has no affect on it at all), and one of the more common observations on this planet is that people and things don't generally leave the surface without external causes.

So all that happens is that Object A (Dentar Thurdent)'s inertia causes him to continue "forwards" whilst the earth's gravity continues to pull him "downwards" so that he either slips, skids or tumbles in an easterly direction until friction dissipates his momentum (in the process imparting a small angular momentum to the planet).

Of course in this case the slipping/skidding/tumbling would be rather brief, as after roughly a third of a second he would impact with the reinforced bakery wall of Object B with what one would presume to be a resoundingly terminal "splat". It would be rather messy, but again only briefly as the body of water formerly claiming domiciled tax status as "the atlantic ocean" would be over-running the area in a huge tidal wave approximately 15 minutes later* and would wash away pretty well all trace of Dentar as well as making the in-store bakery's bread rather salty.

There may be some consolation to be had from the fact that his impact would also impart a small angular moment to the planet, so Dentar Thurdent would have left a tiny, but permanent, legacy to mark his brief and otherwise pointless existance.

Bottom line? There is nothing in the concept of a sudden end to the rotation of the planet that would inherently cause any object on (or part of) the planet to be thrown "upwards" (with respect to the planet's surface) without some external factor such as a ramp or violently irritable bowel condition.

PDR

*Prediction based on typical wave-progression assumptions without experimental verification. Wave progression speeds can go down as well as up. Your home could be at risk if you give too much weight to approximated models; you should consult a qualified and registered wave progression advisor.

1033087.  Mon Nov 04, 2013 11:39 am

 PDR wrote: But then we knew this anyway, because this would be true even *before* the earth stopped rotating (in fact the cessation of rotation has no affect on it at all), and one of the more common observations on this planet is that people and things don't generally leave the surface without external causes.

This was something that occurred to me after I'd done the maths, but it served as a useful checksum to reassure me that I'd got my figures straight :)

(I've not seen the episode yet, so I don't know how much of my explanation was used)

Although having something suddenly stop under you (e.g. having the motorbike you're on suddenly hit a wall) feels like you're being accelerated over the top of it, in fact you're simply continuing to move at the same speed as you were before the thing stopped.

In the case of the Earth, since you're not currently being flung off into space by the force of its rotation, then you won't be flung off into space if it suddenly stops rotating. You'll merely carry on travelling at the same speed you're travelling now, which is demonstrably not enough to fling you into space.

 1033091.  Mon Nov 04, 2013 11:54 am Watching this episode my blood began to boil as i saw the dreaded pile of hokum known as the space elevator begin to rear its ugly head. Instead we were treated to Stephen (or elves) making a massive schoolboy error - which is related to the massive schoolboy error that lies behind the elevator: "If stephen was 44,000 miles tall his CofG would be outside earths gravitational field, ergo he would be weightless." mass of a body acting at a point located at the CofG of the body is a convention employed when teaching physics to the terminally dim. the gravitational effect of the mass of a particle making up a body acts from where the particle is - summing the second moments of all such particles results in the 'mass acting at a point' convention. In this case the body in question experiences differing gravitational attraction depending on the location - an effect so small in everyday experience that it can be neglected. in the case of a 44,000 mile tall man it cannot be ignored. the soles of his feet would experience g of 9.806 m/s while his knees might experience g of 7.5something m/s and the top of his head would see g of nought point bugger all. Summing all these would result in a weight of considerably more than 0

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