Q: If the world were to stop spinning, would the people and everything on it be considered ‘lighter’ or ‘heavier’? Would any change take place? And does centrifugal force have an effect on gravity?

Physicist: Centrifugal force* due to the spinning of the Earth is certainly a measurable effect, but it’s a small effect.  While the spinning of the Earth doesn’t directly affect gravity, it does off-set it a little.  At the north and south poles objects weigh exactly what they should, and at the equator things weigh slightly less.

Assuming that the Earth is round (which is a pretty good assumption), with a back of the envelope calculation you can figure out the centrifugal force trying to fling you into space.  At the equator (where it’s strongest) that force is approximately 0.35% as strong as Earth’s gravity (0.0035 g’s).  So, if you weigh 300 pounds in Ecuador you’ll find that you weigh almost 301 pounds at the Amundsen-Scott South Pole Station.  0.35% doesn’t seem like much, but it would have a profound affect on at least a few historical events.

Centrifugal force always points out from the Earth’s axis, whereas gravity always points toward the Earth’s center.  So you’d think that somewhere between the poles, where the centrifugal force is zero, and the equator, where it points straight up, that there would be a place where it points a bit sideways.

The farther you are from the Earth’s axis the more centrifugal force you’ll experience. At a latitude of ±45° it pulls sideways more than anywhere else.

Turns out, that place is at 45° north and south latitudes where you “should” find that things get pulled sideways with a strength of half of the maximum: 0.17% g’s.  If the Earth was perfectly round, then this would be exactly the case, and everything in Europe would have to be built slightly tilted (if you’re wondering, the Tower of Pisa would be leaning the wrong way).  However, fluids (and the ground is basically a fluid) move so that the net force always points directly into their surface.

A spinning trough of water. Gravity points down and is constant, while the centrifugal force points out and increases with distance. The surface of the water is always perpendicular to the combined force.

By being distorted a little (an extra 20 km at the equator) the combined gravitational/centrifugal force always points straight up and down.  So, if the Earth were to stop spinning right now then we’d find that buildings were tilted very slightly, things at the equator would suddenly weigh 0.35% more, and eventually the Earth would settle into a more perfectly spherical shape.

Now, if the Earth were to literally come to a sudden and abrupt stop: that would be lots of bad. Things at the poles would be fine, but the closer to the equator the greater the change in speed.  At the equator everyone and everything would suddenly find themselves moving east at mach 1.4 (1,038 mph), and every land mass near the equator would be thoroughly scrubbed by the oceans washing over them.  The economy would take a real hit if the Earth suddenly came to a stop.

*Any time that centrifugal forces are mentioned in the vast crucible that is the internet, a small but vocal cadre makes it known that the centrifugal force isn’t really a force.  Be cool.

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58 Responses to Q: If the world were to stop spinning, would the people and everything on it be considered ‘lighter’ or ‘heavier’? Would any change take place? And does centrifugal force have an effect on gravity?

  1. Joseph says:

    It is kind of crazy how many people have no knowledge or vastly incorrect knowledge of how gravity works. As mentioned by one or two above, gravity is a perceived effect caused by curving space. Mass causes this curve, so mass causes gravity. Electro-magnetism has nothing at all to do with gravity, and the spin of the earth actually slightly reduces our perception of gravity since the spin is pushing us AWAY from the surface. Artificial gravity is caused by rotation, but it creates a force pushing out–you stand on the inner surface of the rotating region so that the force pushes you into it.

    Flatness of the earth is easy to disprove. Just look at the horizon, and you can see how objects come into view over the curved surface. Columbus knew that the earth was round because sailors could see masts of distant ships over the horizon before the actual ship came into view. Give some credit to thw greeks. They did a pretty good job calculating size and shape of earth a rather long time ago.

    Now I am just a history major with no degree or anything, but I actually remember things I am taught and generally understand them. Humorously enough, the original opposition to the Big Bang theory was fears by committed athiestic scientists that a Big Bang origin left too much room for God, stop with the silly anti-religion stuff and focus on fact. And with science the most basic fact to understand is that everything you hold as fact will almost certainly be refuted by future sciencists. Stop holding onto fact so religiously.

  2. someone says:

    That is absolutely crazy what would happen if the Earth came to a sudden stop!!! I have an even more interesting questions though. What would happen if the earth slowed down little by little? A smooth slow down not a sudden stop? Wouldn’t night and day stop?

  3. Joseph says:

    If Earth stopped rotating, night and day would still exist–part of the world would still be facing the Sun and part away–but the period would be changed. Each day or night would last around 6 months instead of 24 hours.

  4. Manpreet says:

    If the earth stops rotating the day and night not caused.Day remains day and night remains night so rotation is very important.

  5. Jonathan says:

    Actually if the Earth stopped rotating every 15 days would be equivalent to 1 hour because it would not rotate on its axis but it’s still goes around the Sun. It would not be locked in place by the sun with One Direction pointing to the sun all the time.
    Look at it like are moon it rotates on its axis every twenty-seven days in the opposite direction that it rotates our planet a little more than 27 days giving the appearance of the Moon only has one side looking at us at any given time all over the world.

  6. Harish Dobhal says:

    One more thing to consider, the effect on angular momentum.

    Angular momentum is conserved and if earth stops rotating there will be a change in the orbital angular momentum which would create a change in the orbital path of the earth around sun!

  7. Terry Crevia says:

    How much would the earth’s rotation slow and what impact on the earth’s revolution or path around the sun if and when the north and south polar regions melt due to global warming and water moves to equaltorial region. The angular momentum is similar to an ice skater changing the position of the arms from sides to over head This question is a take off of the comment by Harish Dobhal

  8. Kurt says:

    Melting ice would probably not have much of an effect on the rotational/angular velocity of Earth. The Earth is 6,371,000 meters in radius, and most of that is dense Earth. If the ice caps melted. That would only be about an additional 200 meters in water levels. I could do inertia and momentum calculations but too lazy sorry lol.

    If the Earth stopped spinning I would be more worried about the change of the energy of the Earth. If all that kinetic energy was suddenly gone from the Earth and everything on it, then the energy of the spin of the Earth which was keeping the Earth shaped slightly larger near the Equator would suddenly dissipate. This would lead to 2*10^29 J being released and would likely annihilate the crust surface of the Earth. That’s 10^12 times more energy than the most powerful hydrogen bomb ever detonated. That’s equal to 552 seconds of the total output of the Sun. That’s equal to 5.5 of our moon dropping out of orbit and colliding into us.

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