Journey to the Center of the Earth

Since at least 1898, a problem concerning the time an object would take to travel along an Earth diameter (or a chord) has been appearing in general physics and mechanics books. However, it is always assumed that the density of the Earth is constant and it is not rotating. Using an actual geophysical model of the Earth's interior and a simple spreadsheet formulation, a more reasonable figure of 38 minutes (one way) is determined, compared to 42 minutes for the homogeneous Earth.