At the equator the radius of the earth is 6,378 km, so its circumference is almost exactly 40,000 km.
Imagine we had a long rope which went around the equator, this would of course be 40,000 km long.
If we now placed 1-metre sticks vertically all the way around and lay the rope on top of these sticks (so the rope would be 1m higher all the way around) how much extra rope would we require?
Answer
6.28 metres, a lot less than you might think!
If we call the radius of the Earth R, then the difference between the two circumferences is:
2 x π x (R + 1) − 2 x π x R
= 2 x π metres
= 6.28 metres.
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Puzzle 20
Last week I travelled from London to Leeds, a distance I measured as 174 miles.
I started at 9.15am and completed the journey with an average speed of 40 miles per hour.
On the way back, in the evening, I travelled exactly the same route, starting at 5.15pm. The traffic was light, and I completed the journey with an average speed of 60 miles per hour.
What was the overall average speed for the round trip?
