Space explained
Why don't we feel the Earth spinning?
It is not that the motion is too slow to feel. It is that steady motion, given how we are built, cannot be felt at all.
In brief
We don't feel the rotation because our senses detect changes in speed, not speed: Earth turns at an extremely steady rate and drags the air, the oceans and us along with it. It is the same reason you can walk down the aisle of a cruising aircraft as if you were on the ground.
Key points
- At the equator rotation carries us at about 1,670 km/h; the motion around the Sun adds roughly 107,000 km/h.
- The human body has no speed sensors, it has acceleration sensors: uniform motion is indistinguishable from rest.
- Earth spins because the cloud of gas and dust it formed from was already spinning, and in a vacuum almost nothing slows it.
- The rotation can be demonstrated without leaving the atmosphere: Foucault's pendulum, the deflection of winds, geostationary satellites.
- The day has not always been 24 hours: the rotation is slowing, by about one and a half milliseconds per century.
You are reading this while travelling at more than a thousand kilometres an hour. In Italy, Earth’s rotation is carrying you eastwards at about 1,200 km/h, and at the equator the speed would be around 1,670 km/h. At the same moment the whole planet is running around the Sun at roughly 107,000 km/h. You feel nothing, and you have no reason to feel anything.
The body does not measure speed
That is the whole point, and it is worth stating bluntly: we have no speed sensors. We have acceleration sensors, that is, sensors for changes in speed. The inner ear registers swerves, braking, turns, climbs. Uniform motion produces no signal at all.
You have been through this many times. A cruising airliner travels at about 900 km/h, and in the cabin you pour coffee as you would in a café. You do not perceive the 900 km/h: you perceive the moment the aircraft accelerates down the runway, and when it hits turbulence. Close your eyes with the engines quiet and there is no experiment that can tell you whether you are flying or parked at the gate.
Earth’s rotation is even steadier than an airline flight: no change of heading, no air pockets, a rate that varies by fractions of a millisecond over years. And above all it carries everything with it: the atmosphere, the oceans, the buildings, us. There is no headwind, because the air turns with us. It is a condition with nothing to compare against, and without comparison there is no perception.
A small effect does exist, in fact: rotation imperceptibly reduces the weight a scale measures, and the reduction is greatest at the equator. We are talking about a couple of hundred grams on a seventy-kilo person, roughly 0.3 per cent. It is not something you feel, it is something you measure.
Why does it spin? Nobody pushed it
The question demands a present-day cause, and there isn’t one: rotation does not need to be maintained, it needs not to be stopped.
Earth formed from the collapse of a cloud of gas and dust that was already rotating. As it compressed, a rotating mass spins faster, for the same reason a skater speeds up when she pulls her arms in. That initial motion has never been dissipated, because in a vacuum there is no meaningful friction: only the tides, which act with extreme slowness.
That is why almost every body in the solar system rotates, and why almost all of them rotate the same way: they inherited the spin of the same disc. Rotation is not an engine, it is a leftover.
How it is proven, without leaving the ground
If you cannot feel it, how do we know? The evidence is within anyone’s reach.
Foucault’s pendulum. In 1851, in Paris, a 67-metre pendulum was hung from the vault of the Panthéon. A pendulum keeps the plane in which it swings, so if the floor beneath it rotates, the plane of oscillation appears to turn slowly relative to the room. That is exactly what is seen, and the rate at which it turns depends on latitude. It is the most direct demonstration there is, and many science museums still have one running.
The deflection of winds. On a rotating planet, anything moving over long distances appears to deviate: to the right in the northern hemisphere, to the left in the southern. It is why low-pressure systems wind into spirals, always the same way in each hemisphere. Anyone flying or sailing long routes has to account for it.
Satellites that stay put. A geostationary satellite stays above the same point on the ground because its orbital period matches Earth’s rotation exactly. Every dish pointed at a television satellite is a daily verification: if Earth did not turn at precisely that rate, the satellite would not hold still in the sky and the dish would need constant re-aiming.
The day has not always been 24 hours
One last detail, among the finest. Relative to the stars, Earth completes a turn in 23 hours and 56 minutes, not 24: NASA’s fact sheet gives a rotation period of 23.9 hours. The four-minute difference exists because we have meanwhile moved along our orbit, and bringing the Sun back to the same position in the sky takes a little extra rotation. The 24-hour day is a solar day, not a full turn.
And that day is getting longer. Tidal friction slowly transfers energy from Earth’s spin into the lunar orbit: the Moon moves a few centimetres further away each year and we slow by about one and a half milliseconds per century. It sounds like nothing, but over geological time it changes everything: reconstructions from sediments indicate that hundreds of millions of years ago the day was several hours shorter.
So the full answer is double. We don’t notice the rotation because it is steady and carries us with it, and we don’t notice that it is changing because it changes too slowly for a human lifetime. Neither of those makes it any less real.