If Earth stopped rotating, would this affect the force of gravity?
Chris Daniel
Glan Conwy, UK
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When Earth rotates as normal, the centripetal acceleration of the ground under your feet at the equator has the net effect of reducing the force of gravity on you, so you about 0.3 per cent less than would be the case with gravity alone. This effect decreases with distance away from the equator and becomes zero at the poles. The centripetal acceleration is always perpendicular to the axis of Earth’s rotation and points away from the local vertical towards the equator by an angle equal to the latitude.
In London, for example, which is at a latitude of about 51 degrees north, the combination of gravity and the centripetal acceleration means that you have to lean to the north by nearly a tenth of a degree to maintain your balance. However, you don’t notice this because everything else is also aligned to this apparent local gravitational direction. If Earth stopped turning, you could happily return to a perfectly vertical position with the centre of the planet directly beneath you.
Earth is, as we are taught, an oblate spheroid, which means it bulges at the equator due to its rotation. , its diameter is about 42 kilometres greater than at the poles. This means that the gravitational acceleration at the equator is slightly less than elsewhere because it is further from the centre of Earth. If our planet stopped spinning, it would gradually assume a more spherical shape and gravity would be the same everywhere apart from local variations due to Earth’s non-uniform geology and topology.
However, if it were stationary, the effects on the force of gravity would be the least of your worries. If, say, Earth grinds to a halt over 24 hours, the horizontal deceleration at the equator would be equivalent to about one-two thousandth that of gravity as the rotational velocity goes from about 1670 km/h to zero. While this may not be very noticeable to you, the stress on Earth’s crust could create earthquakes and large surface movements such as landslides. Even more seriously, the oceans would begin to overwhelm the land as water is driven in an easterly direction by the deceleration of Earth underneath it. At the equator the forces on it would be about 5000 times greater than the tidal forces due to the moon.
Weather patterns and ocean circulation caused by Earth’s rotation and diurnal temperature variations would quickly cease. The side left facing the sun would exceed the boiling point of water and the dark side would lose heat into space, cooling enough to cause nitrogen and oxygen to freeze. anywhere. A spinning Earth is better for all of us.
Ron Dippold
San Diego, California, US
Gravity itself would be unchanged, but things would seem slightly heavier. When Earth is spinning normally, things at the equator experience the normal pull of gravity, but there is a centrifugal force counteracting it, like someone hanging off a spinning playground roundabout feels they are being pulled away from the centre. Because of this, things at the equator (which is rotating at about 1670 kilometres an hour) experience a 0.34 per cent apparent reduction in the force of gravity. This effect falls off as you go further north or south, of course. Things at latitude 60 degrees are “only” going about 840 km/h and the rotation isn’t perpendicular to Earth’s surface, so their apparent weight is reduced by about 0.08 per cent. At the poles, the impact is zero.
This is known as the Eötvös effect, after Hungarian physicist Baron Loránd Eötvös, who noticed in the early 1900s that sensitive gravity readings on ships travelling east were higher than on ships travelling west. You are noticeably (with sensitive equipment) changing your apparent gravity when you drive east or west because you are changing the speed at which you are “orbiting” Earth!
Finally, if Earth stopped rotating instantly, most things would be dead anyhow, because 1670 km/h to zero is a hard stop. If you didn’t go splat, the firestorms (from 1670 km/h winds) and tsunamis (1670 km/h water) would get you. People at Antarctic bases would be spared (for a while), and they wouldn’t feel any heavier. Some people have all the luck!
Herman D’Hondt
Sydney, Australia
In short, it would have no effect on Earth’s gravity, as it is only caused by mass. As Earth’s mass doesn’t change when it stops rotating, its gravity wouldn’t either.
However, for an observer on Earth, the reality would be (slightly) different. As Earth rotates once every 24 hours, we are subject to a centrifugal force (or rather, an inertial force), pushing us away from Earth. This is largest at the equator and zero at the poles. Hence, if rotation stopped, a person at the equator would feel slightly heavier and the reduction would diminish to zero as they got closer to either of the poles.
Because of this, an 80-kilogram person at the equator, who usually feels a gravitational force of about 785 newtons, would feel an extra force of 2.5 newtons. In other words, our guinea pig would feel about 0.3 per cent heavier – without any change in their mass.
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