Hugging the world
Here's a quick little puzzle that's kinda cool:
Imagine that someone (or, probably many people) managed to tie a rope around the entire world, lying it on the ground across the equator. You could say that the rope literally hugs the whole earth, kind of like the seam of a cricket ball. The question is: How much extra rope would you need to raise the whole thing a metre off the ground around the entire globe?
What's your first instinct? If you like, write down your guess in the comments. To hide the answer from you, you'll have to scroll down. But to make sure you're not disappointed, here's a cool little clip of an intersection in a street in Germany, where pedestrians can play 'Pong' with the pedestrians on the other side while they wait for the lights.
Okay. The answer is: 6.3 metres of extra rope. The question is mathematically straightforward - the extension of the radius (1 metre) has to be multiplied by two times pi - but far more interesting is how our first instincts are (usually) so far off. What was your first guess? Mine was one kilometre. Whoops.