Another video today, this one about what would happen if you dug a hole through the Earth to the other side and jumped into it.

Ignore, for a moment, if you will, the fact that we have yet to manage to dig past the Earth’s crust.  Ignore also the molten magma and other inconveniences of being near the centre of the Earth.

Instead, try to answer this question: how long does it take to fall from one side of the Earth to the other, if you jumped in?

If you’ve watched QI, you may already know the answer, but if not, go watch this video.  Instructional, but also fun.