Probably every physics teacher was asked this question at least once. Of course, such a tunnel is impossible for a variety of reasons that are beyond the scope of this article. Suppose, in some magical way, such a tunnel was nevertheless created and is kept in a stable state.
There are many misconceptions associated with a hypothetical tunnel through the center of the earth.
The main one is that if you drill such a tunnel and jump into it, the jumper will always fly back and forth from one end of the tunnel to the other.
This is not true. More precisely, not quite so. In order for the described scenario to become a reality, three conditions must be met:
In other words, one entrance to the tunnel should be at the North Pole, and the other at the South Pole. Why don’t the other options work?
The earth is known to rotate on its axis. Due to the fact that the absolute speed of rotation of matter slows down as it approaches the center of the Earth, if the tunnel is not completely aligned with the axis of rotation of the Earth, then the jumper will simply crash into the wall of the tunnel and will be smeared over it.
It will be worst for the jumper if the tunnel is drilled at the equator. Then the jumper will crash into the wall without flying even a kilometer.
If the air is not pumped out of the tunnel, then two things will happen, each of which will make such a jump impossible. Firstly, the jumper will slow down a little due to friction against the air, and very soon his speed will stabilize around 200 km / h (a record for the speed of free fall of parachutists). Of course, the final speed will depend on the aerodynamic characteristics of the jumper’s suit, but in general it is unlikely to be much higher.
Having reached the center of the Earth, the jumper will fly over it quite a bit and rather quickly «stabilize» in the center of the Earth.
The second reason is that atmospheric pressure and temperature will build up in a tunnel filled with air. Already at a depth of 100 kilometers, the pressure will exceed the pressure at the bottom of the Mariana Trench, which is less than 1 percent of the way. As a result, the jumper will simply be crushed by the tremendous pressure.
Planet Earth is not a homogeneous body. In some places the density of matter is higher, in others it is less. In addition, due to convection processes in the earth’s core and the movement of magma, these inhomogeneities are constantly moving.
In ordinary life, these inhomogeneities can be neglected, but with a free fall through the center of the Earth, they will inevitably affect the free fall acceleration experienced by the jumper, and through a sufficiently small number of oscillations (several hundred or thousands) they will cause the jumper to «descend» from the distance.
In practice, due to the inhomogeneities of the gravitational potential, the jumper will either a) be smeared against the walls of the tunnel b) will gradually slow down and hover in the center of the Earth.
Actually, for these three reasons, the scenario with the eternal fluctuations of the jumper «back and forth» is not feasible. And if at least speculatively it is possible to imagine that it is still possible to dig a tunnel, keep it in a stable state and pump air out of it, then it is impossible to imagine that humanity will ever be able to evenly distribute the mass of the Earth over its volume.