{
  "title": "Fall through a uniform Earth, every 30 seconds",
  "description": "A car falling from rest straight through the center of a uniform, frictionless Earth: distance from the center (km, negative on the far side) and speed (km/s) every 30 seconds until it stops at the far end after 42.17 minutes, from the closed form and from a step-by-step numerical integration, side by side. Constants from NASA's Earth Fact Sheet (radius 6371.000 km, surface gravity 9.820 m/s^2). Retrieved 2026-10-31. License CC BY 4.0.",
  "license": "CC BY 4.0",
  "license_url": "https://creativecommons.org/licenses/by/4.0/",
  "creator": "Puzzles, Charts & Dilemmas",
  "page": "https://puzzleschartsanddilemmas.com/thought-experiments/gravity-train/",
  "derived_from": [
    "NASA NSSDCA, Earth Fact Sheet (last updated 2024-11-15), volumetric mean radius 6371.000 km and surface gravity (mean) 9.820 m/s^2, https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html"
  ],
  "method": "Compiled by Puzzles, Charts & Dilemmas from the data listed",
  "data_credit": [
    "NASA Earth Fact Sheet (radius and surface gravity)"
  ]
}