Earth question

[Bazile]

Here is a question I was asked recently and couldn't answer properly

The earth is a sphere as you look at it from space - so why is it that if you travelled say from the north pole around it and back to the north pole ( without leaving the surface ) you wouldn't get the sense of moving in a circle ?

Hope you can see what I am getting at

[Gef]

Becuase it is such a big circle and we are not aware of the Earth's curvature from the surface.

[Loosehead]

even if it was perfectly smooth like a Billiard ball the curvatures so slight as to not be noticed, however you would get some ide from the fact that the horizon never seems to move.

[heathfield]

'Cos it looks flat to you. In history, a lot of people had a lot of difficulty in convincing others that the Earth was a sphere. In fact, the Flat Earth Society still exists, with members who still don't believe it's round. See here

[Teddio]

Since you live on a sphere the gravitational field lines are always normal to the surface. (ie. perpendicular) Therefore your weight always acts vertically downwards no matter where you are on the sphere (eg UK or Australia). This helps give the impression that the Earth is flat.
If you were to travel the 24000 miles along a line of longitude from the north pole to the south pole and back again you would notice a shift in the constellations which could only be explained by you moving around the surface of a sphere.

[xud]

Heathfield, I am still laughing at having visited the flat earth website.
That has got to be a wind up, surely!

[xud]

Oh, I forgot to mention.
When in Australia for example, the water flows the opposite way (anticlockwise) down the plug-hole, to what it does in UK

[Bazile]

The person held a football in front of him to represent the earth and stated that there is nowhere on it that is flat , so how can you travel on and around it and do not get the feeling of the curvature .

Pointing to the bottom of the ball as he held it , he wanted to know why people at that part of the earth wasn't
' falling off ' :-)

Thanks for your answers - I will now have another go at explaining it

[Teddio]

In response to XUD's statement, water does not flow the opposite way down the plughole in Australia compared to the UK. The only mechanism which could cause this is the Coriolis Force. This force has no measurable effect on a basin of water but has a huge effect on large bodies of air and is responsible for the opposite rotation directions of anticyclones in the northern and southern hemispheres.

[mibn2cweus]

Millions of people living along the Equator partake in a similar journey every day with no ill effects in spite of moving along at 1667km/h. They do however weight a bit less then they would at the North or South Pole as a consequence of the Earth's rotation.

[Bert]

Not just because of the Earth's rotation, though, perhaps also because of the Earth's rotation, mibn. The Earth is not a sphere, but an oblate spheroid, which maybe because of its rotation. Either way, the radius at the equator is greater than at the poles, so the gravitational force is less because you are further from the Earth's centre of mass.

[mibn2cweus]

effects of rotation on gravity and weight

[chakka35]

Teddio, I think xud was joking. It is, though, astonishing how many people believe this nonsense without ever bothering to check whether the water flows out in their own house (let alone in everyone else's house) in the same direction every time. A friend produced guffaws from me when he said that he'd just returned from equatorial regions and, sure enough, as he crossed the equator his hotel bathrom water flowed out in the opposite direction! I'm not sure that he understood in the end that if the Coriolis Effect did influence these things (which it doesn't) then it would greatest at the poles and zero at the equator. But he did understand that it was 50/50 anyway.

[xud]

Regarding water flowing the opposite way down the plug hole. It's just what I've heard, I had no reason to suspect otherwise.
Are there any Aussie's out there to confirm this or not?
I would love to go to Australia though.
I'm not sure Easy Jet do flights there just yet