Right. So my mother says the world is round. In that case,

[Flightattendant2]

why do the people on the bottom, not feel like the blood is rushing to their heads?

I need to explain this one to ds because me and mum ended up concluding that the earth is actually flat.

we are actually spinning quite fast, or at any rate the people on the equator are!

'The Earth is spinning around its axis. At the equator, the Earth's surface moves 40,000 kilometers in 24 hours. That is a speed of about 1040 miles/hr (1670 km/hr or 0.5 km/sec). This is calculated by dividing the circumference of the Earth at the equator (about 24,900 miles or 40,070 km) by the number of hours in a day (24). As you move toward either pole, this speed decreases to almost zero (since the circumference of the spinning circle at the extreme latitudes approaches zero).'

so at the equator they are going 1 Km every 2 seconds.

and don't forget that the solar system is also moving, as is the Milkyway!!!

dear old monty python say it best , I think!!

surely the world is an oblate spheroid

And nobody falls off because of gravity.

And the world is spinning anyway so what seems to be up is actually not and won't be forever.

Why don't you just tell him the world's flat and rests on the back of 4 elephants standing on the back of the great turtle A'Tuin. That's what I told my kids .. they seem satisified (all hail Pratchett)

Oh dear, I'm afraid I got rather sidetracked there with the lumberjack song...

Fan bloody tastic isn't it?!

Yes Flightattendant the surface of the earth is moving very fast, about 1,000 miles per hour at the equator (less in the UK).

But when you are in an aeroplane you don't feel as if you are travelling at 500mph, because you are travelling in a straight line. Sometimes, when the pilot starts to descend you get a light feeling in your stomach, and then you know you are changing direction. It is the same on a roundabout, when you are going round in a circle you are constantly changing direction and this is how you notice you are moving (and what makes you dizzy). But at the surface of the earth you are changing direction very slowly (one rotation in 24 hours) so that is why you don't notice it.

singleWhiteMale I am afraid you are wrong. A roundabout's motion is constant (ignoring the slowing down due to friction) but we notice that. It is true that we would notice if the earth suddenly stopped: we (and anything else not tied down really well, including the atmosphere) would fly along the ground at 1,000 miles per hour (not vertically up). That couldn't happen in practice of course: any force that was large enough to decrease the angular velocity of the earth at a noticable rate would break up the surface of the earth at its point of action, which would be bad . And the earth's mantle and core would continue to rotate causing turbulance which would break the earth apart, really really bad .

Did I start a scrap yet?

Sorry singleWhiteMale, I didn't mean to say you are wrong, I meant to say that we are talking about two different things.

What you are saying is that you don't notice that you are travelling at 1,000mph (relative to the centre of the earth) because that speed is constant, and that is true. This (together with the direction we are travelling) is called velocity.

What I am saying is that you don't notice that you are rotating (i.e. spinning) because the earth's angular velocity is low (15 degrees per hour).

When you are on a roundabout you know you are spinning not because your velocity is large (about 10mph, or 1% of the velocity of the surface of the earth), but because your angular velocity is (perhaps 90 degrees per second, over 20,000 times that of the earth).

Note for pedants: velocity is used here within the earth's frame of reference; the modulus of the velocity is abbreviated to velocity.

you round-earthers are all the same.
you have no Proof!!! damn you.
who says we are Wrong? It's just a Theory.

Actually MrVibrating, I'm not wrong (actually!).
A roundabout is a completely different kettle of fish. We're not gravitationally attracted to it (not much compared with the earth anyway) so we have to hang on otherwise we'd fly off. We feel disoriented because our eyes are telling us we are going round but our sense of balance says we're suspended face down (assuming we're facing outwards).

On the earth's surface, the planet's rotation has two perceivable effects. First, the faster the earth spins the less we seem to weigh. That's because the centrifugal (pseudo-)force acts roughly opposite to the gravitational force. If the earth sped up so that a day lasted 5 minutes, people living near the equator wouldn't weigh anything - in fact they'd technically be in orbit.

The other effect is coriolis force. As we travel between latitudes we experience a sideways force because we speed up near the equator and slow down near the poles.

So why wouldn't we notice if the earth was spinning faster? Because these effects are really small (unless we take things to ridiculous extremes.) Things would weigh slightly less than on 'our' earth, but so what? Since we'd never experienced anything different everthing would be normal as far as we were concerned. And the coriolis force is so tiny we wouldn't notice it (do you notice it now?) We certainly wouldn't feel that we were on a 'space roundabout'.

x-posted MrVibrating.

That's what I thought you meant. You're still wrong

Thinking about it some more, I suppose you're right(ish)

As long as the earth isn't rotating fast enough for us to experience coriolis force in everyday life, we're not going to perceive it as rotating. Having said that, it would have to be rotating unfeasibly fast before we did.

I'm still not keen on the roundabout as an example though.

I have not seen so many blokes on one thread before.

That's quite interesting.

Well, we all wanted to come out of the woodwork for the "arranging hot lesbo action" one last week but thought it might have looked rude.

Unfortunately roundabouts are the standard model for visualising effects of rotating frames of reference - see here for example. That is because they are the only thing most people have regular experience of where the effects are large enough to be observed (apart from a car on a bend, or a swing; in both cases the transitory nature of the effects, and for the swing the additional effect of the harmonic oscillation, er swinging make them less useful*).

Besides, roundabouts are fun

• talking about swings, flat-earthers please read about Foucoult's Pendulum.

If you watch the NASA video in my last post, the (not very annoyingly American) presenter helpfully points out that the human brain can get used to the coriolis effect even if it is becomes significantly larger.

But the reason you know you are spinning on a roundabout is not the coriolis effect (unless you are throwing a ball), and it is not what you see either (shut your eyes, and you still know). It is the sensations in the vesistibular labyrinth - I love that term - in your inner ear.

Thinking about it, even if the earth were spinning so fast that our balance organs should detect it, we wouldn't do because we would be used to it. So in fact singleWhiteMale, you are right after all - even if the earth were spinning very much faster, we wouldn't normally notice it because the rate of spin would be constant and we would be used to it!

Thanks MrVibrating, I think we're on the same wavelength. I would say that, on the roundabout, the sensations from the vestibular labyrinth mostly occur because of coriolis force acting on the fluid when you move your head. If you kept still you wouldn't feel anything unusual except a centrifugal force apparently pushing you away from the centre which is relatively subtle and could easily be interpreted as your being seated on a slope.