Sue Wong, of Ilam school, asks :-

Megan Gibb, of Ardgowan School, asked:-

If the world is round why is where we live flat?

Graham Batchelor, a yachtsman and physics teacher at Riccarton High School, responded.

If it was flat then it would be possible to fall off the edge. Early sailors thought this was so and lived in fear of the day the ship would do just that. But it never happened. There is plenty of evidence that the Earth is a sphere but none so convincing as photographs taken from spacecraft.

Even though it looks flat the Earth's surface is slightly curved. Try to imagine that you are a small ant standing on the surface of a very large balloon. It would seem nearly flat where you were standing. How much of the balloon would you be able to see? Not much.

If you stand on the deck of a yacht your eyes would be about 2 metres above sea level and you would only be able to see a floating object up to five kilometres away. If you climb 10 metres up a mast you could see 12 kilometres around you. The old pirates knew this which is why they had crow's nests up their masts. Lighthouses are usually tall and placed on top of cliffs so that they can be seen from a great distance.

So next time you are at the beach have a look at the horizon. When you stand at water's edge (your eyes would be about a metre above water level) the horizon is only about two and a half kilometres away. Can you see a ship? If so, notice that you can only see the top part of it because the lower part is hidden below the horizon.