Falling Through Earth Calculator
Calculate travel time, max speed, and weightlessness when falling through a frictionless Earth tunnel using uniform and PREM density models.
The Gravity Train Thought Experiment
Imagine a frictionless tunnel through Earth. Drop an object in and gravity pulls it toward the center, then decelerates it toward the exit. This calculator estimates travel time, maximum speed, tunnel length, and weight experience using uniform-density and PREM Earth models.
Uniform Density Model
Inside a uniform sphere, only mass closer to the center contributes to gravity. Motion is simple harmonic with one-way time about 42 minutes 12 seconds, independent of chord angle. Maximum speed at the core is roughly 7,900 m/s.
PREM Variable Density Model
The real Earth has a dense iron-nickel core and lighter mantle. Gravity peaks near the core-mantle boundary, so travel time shortens to about 38 minutes one way in the PREM model.
Related tools: Banana Radiation Calculator and Gravitational Force Calculator for more physics calculations.
Frequently Asked Questions
How long does it take to fall through Earth?
About 42 minutes 12 seconds one way with a uniform-density model, or about 38 minutes with the PREM density model.
Why is chord travel time the same as a center tunnel?
For uniform density, motion along any straight tunnel is simple harmonic with the same period. Shorter chords have weaker acceleration along the tunnel, so travel time stays constant.
Would you feel weightless during the fall?
Yes. In free fall you experience apparent weightlessness, similar to orbit, because you and the tunnel fall at the same rate.
Does body mass affect travel time?
No, in vacuum all masses fall with the same trajectory. Mass only changes weight force at the surface, not fall time in this idealized model.
Can we build a gravity train today?
No. Core temperature, extreme pressure, air resistance, and Earth's rotation make a full diametric tunnel impractical with current technology.
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