Science
What If You Fell Through the Earth?
Short answer: about 42 minutes to the other side, if Earth had uniform density and the tunnel had no air or friction. You’d pass the centre at around 7.9 km/s. Add friction and you’d stop short instead of popping out.
How long is a gravity-train ride through a tunnel along a diameter?
A straight tunnel through Earth's centre is a seventeenth-century daydream with a clean answer if you stack the right lies. Uniform density, vacuum tunnel, no Coriolis, no magma: the gravity inside a sphere is proportional to radius, the motion is simple harmonic, and the one-way trip is half a period — about 42 minutes, the same for a chord through Earth, famously. Takeoff speed at the centre is orbital-ish, near 8 km/s. Turn friction on, even as a toggle, and the oscillation dies; you do not pop out in Australia. Real Earth is denser in the core, so the true vacuum-tunnel time would shift a little. This page uses the uniform-density formula and says so. It will not drill the hole.
Written and checked by Aivora Digital · Last updated:
Change this
Results update as you move the controls.
Off: you do not oscillate, you do not exit the far side.
Your result
42.2 min
one-way through a diameter
uniform density, no friction
- One-way
- 42.2 minutes
- Round trip
- 84.4 minutes
- Peak speed at centre
- 7,904 m/s
- g used
- 9.81 m/s²
- Friction
- ignored
42 minutes 12 seconds
28,456 km/h
What does that mean?
In the uniform-density vacuum tunnel, one-way time is 42.2 minutes (T/2 = π sqrt(R/g)). Peak speed at the centre is 7,904 m/s. At 1× surface g the clock scales as 1/sqrt(g). Turn friction on and this harmonic story ends: you would not come out the other side. Real Earth's denser core would tweak the 42 minutes, not replace them with a Hollywood core of lava-surfing.
At a glance
- One-way42.2 min
- Round trip84.4 min
Timeline
0
Step in
Weight is still mg. The tunnel is the fiction.
21.1 min
Centre
Speed peaks at 7,904 m/s. Gravity is zero at the exact centre in this model, but you are moving too fast to linger.
42.2 min
Far side
If the other hatch is open and the vacuum held, you arrive at rest — then fall back, forever, in the ideal oscillator.
Compare scenarios
Why 42 minutes
Inside a uniform sphere, gravity at any depth = surface gravity × (distance from the centre ÷ R). That is Hooke's law. Period is 2π sqrt(R/g), one-way is π sqrt(R/g). Plug in mean radius and standard g and you are near 42 minutes. Raise g with the multiple slider and the trip shortens as 1/sqrt(g). The same period shows up as a low-Earth-orbit period for a grazing circle, which is not a coincidence: both are sqrt(R³/GM) in disguise.
The middle is fast
Energy conservation puts your peak speed at the centre: v = sqrt(g R) for this model, around 7.9 km/s on Earth. That is not a sightseeing pace. It is also why 'just jump in' is a thought experiment. Air would turn the tunnel into a furnace; rock would not permit a hole; Coriolis would slam you into a wall on a rotating planet. Those are the reasons the toggle labelled ignore friction is on by default.
Friction ends the joke
With drag or with a medium in the way, you dissipate the potential difference between surface and centre. You do not climb the other side. In a cartoon of strong friction you stop somewhere short of the far exit, perhaps near the centre if you leave enough energy on the table. This page does not integrate a drag coefficient. It changes the story from 'oscillator' to 'you do not come out.' That is the scientific punchline once you remove the vacuum.
Common questions
How long would it take to fall through the Earth?
About 42 minutes one way, using a uniform-density Earth and a tunnel with no air or friction. Real Earth is denser in the core, so the true figure would shift a little.
How fast would you be going at the centre of the Earth?
Around 7.9 km/s, close to the speed of a low orbit. That’s where your speed peaks before you slow down on the way up the other side.
How we calculated this
One-way time = π × √(R ÷ g), where R is Earth’s mean radius and g is surface gravity times the multiple you choose. Peak speed is √(g × R) in the frictionless, uniform-density model. If air and friction are switched on, the result says you would not oscillate or reach the far side, rather than showing a made-up figure. Not a PREM density profile, not a rotating-Earth Coriolis integrate.
Assumptions and limitations
This is a simplified estimate. Actual results depend on factors the model does not include.
This is a simplified thought experiment. It uses transparent assumptions so you can see what changes — it is not a full physical simulation of the real world.
- Earth is a uniform-density sphere of the IUGG mean radius.
- The tunnel is a vacuum diameter unless the friction toggle is off.
- Coriolis, magma, and structural strength are ignored.
- With friction, there is no simple-harmonic return; you do not pop out the other side.
- The gravity multiple scales surface gravity rather than rebuilding the planet.
Sources
- NIST CODATA — standard acceleration of gravity
gn = 9.80665 m/s².
- NASA Earth fact sheet
Earth mass and radius for orbital and gravity-train numbers.
- NOAA NGS — WGS 84
Earth's equatorial figure; the train formula uses the IUGG mean radius.
Go further
Related experiments that pick up where this one leaves off.
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