18th Dec 2012

Free Fall through the Earth

In the late 17th century, British scientist Robert Hooke wrote to Isaac Newton and discussed the mathematics of a thought experiment—one where an object was dropped down a tunnel drilled through the earth. He was fascinated by the physics of it: For the first half of the journey, gravity would pull the object into free fall. It would accelerate until it reached the midway point, where it would decelerate because it would be climbing away from the centre of the earth—and yet in a completely frictionless environment, it would have exactly enough inertia to reach the opposite end of the tunnel before it stopped completely. If the earth was a perfect sphere and the tunnel was frictionless, the trip would always take exactly 42 minutes and 12 seconds no matter at what angle the tunnel was drilled. Of course, this perfect scenario doesn’t exist in the real world, but the thought experiment still presents a dazzling engineering prospect—an incredibly fast transportation system (say, a train). Building this “Gravity Train” was first proposed in the 1800s, but the Paris Academy of Sciences wisely declined the ambitious plan—and even now, the concept is seemingly out of reach. Billions of cubic metres of rock would have to be hauled away to even drill the tunnels, the extreme heat and pressure of the core and mantle would present a huge problem, and measures would have to be taken to minimise friction. Transporting cargo between continents seems like a more feasible outcome than transporting humans, but we can hope that some incarnation of this Gravity Train will come into the realms of possibility before another four hundred years has passed.

(Image Credit: 1, 2)

This post has 292 notes
  1. rickyhitler reblogged this from sciencesoup and added:
    Another issue would be the extreme speed at which the train is travelling. We already have to prepare astronauts and...
  2. drewbert7 reblogged this from sciencesoup
  3. cutegirlshavemorefun reblogged this from sciencesoup
  4. astronomical-indie reblogged this from sciencesoup
  5. helenorvana reblogged this from sciencesoup
  6. affectionitmatters reblogged this from sciencesoup
  7. blackprinz reblogged this from sciencesoup and added:
    Free Fall through the Earth In the late 17th century, British scientist Robert Hooke wrote to Isaac Newton and discussed...
  8. clariel-ideasthetic-fallen-angel reblogged this from farmergerald
  9. nickelsissocool reblogged this from sciencesoup
  10. noaa131 reblogged this from older-and-far-away
  11. older-and-far-away reblogged this from noaa131
  12. matthewholmes12 reblogged this from sciencesoup
  13. jack-of-all-the-trades reblogged this from sciencesoup
  14. nighttimewanderings reblogged this from thepiratedragon and added:
    I would like to point out that the outer mantle also generates the Earth’s magnetic field, so no metal in your train....
  15. aboatmadeofdreams reblogged this from sciencesoup
  16. thepiratedragon reblogged this from sciencesoup
  17. farmergerald reblogged this from sciencesoup
  18. biggestdweeb reblogged this from polarbearking
  19. fishjellies reblogged this from sciencesoup
  20. ironicallytheybecamegods reblogged this from animanga90
  21. animanga90 reblogged this from sciencesoup
  22. dr-windes reblogged this from sciencesoup
  23. hijosdebabilonia reblogged this from sciencesoup
  24. keyjackdiamonds reblogged this from kingofspacetime
  25. kingofspacetime reblogged this from sciencesoup
  26. jvdbooks reblogged this from sciencesoup
  27. eyeofmairon reblogged this from sciencesoup