h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is an interesting idea that does indeed rely on the principles of Newtonian gravitation and Hooke's law, but it ignores a staple of mechanics that is not taught in introductory physics courses: the Coriolis force. This is the same physical force that is responsible for trade winds and yes, the direction in which water swirls when going down a drain (though not in toilets, as the myth goes; toilets swirl because they are designed to).

The Earth is a sphere which is spinning around a single axis. Imagine that you live along the equator, and you want to try this gravity sled thing so you can zoom to the other side. What happens to you? You'll end up crashing into the side of the tunnel. On Earth rotates at a constant ANGULAR speed of one rotation per day. But the speed at which you are moving for that rotation depends on your distance from the axis of rotation. The farther you are, the faster you're moving (imagine a spinning wheel - the rubber around the tire is definitely moving faster than the metal of the hub). As you dive towards the center of that axis, you're STILL moving as fast as you were on the outside, but suddenly the ground around you is moving slower. The end result? You're going to begin accelerating into the side of the tunnel.

Thus, the gravity sled could only truly work - even in theory - if you were travelling straight along the Earth's axis.

Well, as true as this is, and as well documented the effect is, that is why the sled must be frictionless. It doesn't matter if you are in constant contact with all sides, as long as friction has been eliminated.

True, elimination of friction is an ideal, unlikely to be accomplished; but then, so is the excavation of the tunnel. Added propulsion upon entry or exit could make up for any loss, as mentioned in the entry.

The really interesting point is that it works at any angle, not just through the center. The effect would be nullified if the tunnel was cut in the direction of the spin.

Aaaahhh, the infamous phantom researcher?!

Looks like you signed on just to comment on this entry, eh?

Hope you come back. We welcome controversy here.