Suppose you dug a tunnel through the center of Earth, jumped in, and let gravity pull you through. If someone were to drill a hole all the way through the planet, and then somehow manage to fall into it, how long would it take them to arrive on the other side? For decades, physics students have been asked to calculate that time and have been taught that the correct answer is 42 minutes. "This is the kind of paper we love," says David Jackson, a physicist at Dickinson College in Carlisle, Pennsylvania, and editor of the American Journal of Physics, a publication of the American Association of Physics Teachers. Credit: NASA (Phys.org)—Alexander Klotz a student at McGill University in Canada has calculated a new answer to the commonly asked physics question, how long would it take a person to fall all the way through the Earth? To get a more realistic mass distribution for Earth, he relied on the Preliminary Reference Earth Model, which is based on seismic data. He has used seismic data to calculate the different densities at different depths and has used that data to give a more accurate answer to the falling man question, stating that it would in fact, take just 38 minutes (and 11 seconds) to fall all the way through, not 42 and (12 seconds). Curiously, Klotz found that he got almost exactly the same answer—38 minutes flat—if he simply assumed that the force of gravity remained constant and equal to the value at the surface as an object plummeted toward the center. Although the assumption of uniform density works well in many cases, the simpler assumption of a constant gravitational field serves as a better approximation to the true results. For his part, Klotz says that, in this day of big science, his experience shows that "with the right idea it's still possible to make, not a monumental discovery, but an incremental one."
– It's a common hypothetical in physics classrooms: How long would it take to fall through a tunnel from one side of the Earth to the other? The new answer: 38 minutes and 11 seconds, reports Science. The result is courtesy of McGill University graduate student Alexander Klotz, whose calculations take four minutes off the previously accepted answer and appear in the American Journal of Physics. The reason for the shorter time? Unlike previous calculations, Klotz's take into account that the Earth's layers have different densities, and those differences would affect the hypothetical falling man, notes Phys.org. "The way the Earth is structured, the gravity increases slightly as you go deeper towards the dense core, to about 110% of its surface value, before getting weaker as you move through the core, reaching zero at the center,” says Klotz, as quoted in Forbes. (If it's all a little too hypothetical, try physics-inspired pasta instead.)