Michele Murray, age 16, of Youngstown, Ohio,n for her question:     

Could a tunnel be dug straight through the earth?

At present, this fascinating project is absolutely impossible. It is doubtful that engineers of future centuries will have the skills and power even to plan it. But we can . dream and speculate about it and along the way we may gather some odd bits of information about the earth.
A tunnel through the earth is a wonderful idea and almost everybody has thought about it. Since the globe is round, it seems logical to drill a hole straight through the middle. On a wintry day, we can lounge in an armchair and dream of a subway leading down, straight down to a sunny beach in Australia where, of course, the Southern Hemisphere is enjoying its summer season. Since gravity pulls things down, it seems logical to suppose that our subway capsule would need no power to fall through the globe. The problems involved, however, are so numerous and so immense that our wonderful dreams cannot possibly be realized.
In the first place, the tunnel would have to pass through the heat and demos materials of the earth's interior. The distance is almost 8,000 miles and things get worse as the tunnel deepens. At the exact center, the pressure is estimated to equal a weight to 20,000 tons on each of the six sides of a cube. The temperature is estimated to be something between 4,000 and 8,000 degrees Fahrenheit.
Digging through such weight and heat is hard to imagine but at least to this point gravity has been our friend, helping us down. At the center of the globe, however, we reach the center of gravity and the pull reverses direction. We now must tunnel upward.' Let's pause here for a moment and consider the problems of locating the tunnel.
The earth rotates on its axis, which runs from pole to pole. Every part of the globe, the surface and the deep interior, spins around this line through the middle. This spinning force would be felt by the tunnel diggers. In a tunnel on a line with the equator, we would have to fight a strong and constant shove to one side.. Farther north and south of the equator, this sideways shove would lessen, but it still would tend to veer the tunnelers to one side. What's more, if we ever completed our impossible tunnel, this rotational swerve would bash anything traveling through it against the walls. There is one, and only one way to avoid this problem. We must plan to, take advantage of the earth's  axis and dig our tunnel in a straight line through the center from pole to pole. This is the stationary axis around which the rest of the spinning globe rotates.
If we really stretch our imaginations, we can see our tunnel completed, all ready for a capsule to fall in a straight line about 7,800 miles long. The first half of the trip whizzes by with the acceleration speed of a falling stone, or thereabouts. At the center of the earth the capsule's velocity is tremendous. But here it encounters the pull of gravity, and it must push its way upward. Its speed carries it quickly up, up for a thousand, two thousand miles. But gravity slows it down with every step of the upward journey. Near journey's end, the capsule is traveling at a snail's pace. At ground level it stops and falls back to the center of the earth.     `
On the return journey, the acceleration and deceleration would be repeated in reverse. The capsule would reach maximum speed at the earth's center and decelerate at the same rate through the second half of the journey. We could, of course, attach an auxilliary motor to shove the capsule up the last lap of the tunnel. If we did not do so, the capsule and its passengers would continue to swing up and down, back and forth, like pendulums, forever.