A straight line on the Earth’s surface is not straight!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

26 April 2009

In this day and age, we shouldn’t be discussing whether the Earth is round or flat. Not with all the photographic evidence provided by astronauts and cosmonauts who travel to outer space and look “down” on our planet. But then I guess if we didn’t argue things out, life would be boring. This probably explains why the Flat Earth Society is still alive and well.

In that light, Peter Wanjohi asks some interesting questions and I am sure he is not the only person who has wondered about them: “If the earth is a sphere – barring mountains, valleys and oceans – (a) why is it possible to construct a storied building spanning the whole earth's surface? (b) Why would men lined up shoulder to shoulder along a longitude around the earth, not tilt towards the ground progressively towards the poles? (c) Why would an aircraft on auto-pilot flying in a straight line above sea-level not veer off in a tangent into space?”

The answer to the first question is that if such a building were constructed, the upper floors would have to be made slightly longer to accommodate the increased distance from the centre. From space, it would look like a ring around the planet.

The ground floor of such a building would be 40,192km. This is simply the equatorial circumference of the Earth based on the average diameter of 12,800km. Every additional floor would have to be longer because it would span over a larger diameter…like the lanes in the race track of a stadium.

Assuming that each floor is about four metres high, the total height of, say a ten storey building comes to about 40m. Thus the diameter at the top would be 12,800.08km, giving a circumference of 40,192.25km….this is 250m longer than the base.

The second question is related to the first; and yes, a large number of men (about 80 million of them) can stand shoulder to shoulder all the way around the Earth…without tilting “progressively towards the poles”. The reason is that, at an average height of 1.75m, the circumference at their heads would only be about 11 metres longer than that of the Earth.

Now human beings are normally broader at the shoulders than at the feet…they look like inverted trapeziums! My width at the feet is about 25cm, while at the shoulders it is 55cm. This shape can easily accommodate the extra 11m if the people were standing in a “line” (actually; it would be a circle) around the Earth.

Regarding the last question, the answer is that if the aircraft did indeed travel in a straight line, it would veer off at a tangent into space. However, if it maintained a constant height above sea-level, then its path would NOT be a straight line!

The sea (which covers about two-thirds of the Earth’s surface) is curved onto the spherical shape of the planet. Thus an aeroplane maintaining a constant altitude would follow path parallel to that of ship on the water surface.