Walk out your front door and keep going for 24900 miles, then explain to me why you are now standing outside your back door if the earth is flat
Dave
OK, so lets run with this experiment.
Dr Dave sez, if I walk in a straight line for 24,900 miles I will end up back at my house. (I intend to run, it will save time)
But to show the Earth is round, I would have to conduct this experiment at different latitudes, travelling due east (or west) each time, with each circuit of the globe being shorter and shorter (see the drawing below, on the left).
I will assume that when Dr Dave sez 'keep going' he means in a straight line. Which because the Earth is round would mean at some point after leaving home, I would actually leave the surface of the planet, (see picture on the right), otherwise my path would not be straight, but curved. (It's a 3 dimensional world we live in)
Be that as it may, I will still work with the original game-plan.
Now, if we assume that the Earth is round, the North Pole is only really an arbitrary point, so to make things easier, I intend to base my 'walks' around a point in my back garden. So, instead of the top most point on the original drawing being the North Pole, it is the pear tree in the back garden. And instead of the longest circumference first, I will start with the smaller ones nearer the pole/pear tree. (getting some good data in quickly is always a good thing in research)
So, in a nutshell, Dr Dave's experiment to show the world isn't flat involves me running round and round the pear tree in ever decreasing circles while flapping my arms vigorously shouting "I can fly, I can fly"
Fortunately it's raining at the moment, so I won't conduct this cutting edge research just yet.