Anyone who has ridden a merry-go-round knows the feeling. The faster it spins, the harder you have to hold on, or you'll go sailing off the edge. Our planet is spinning too, and much faster than any playground ride. So why aren't we all sliding off into space?
Here's the short answer: gravity is far stronger than the outward effect of Earth's spin. The rotation does pull on us a little, enough to make you weigh about 0.3 percent less at the equator than at the poles. But Earth's gravity easily wins that tug-of-war, so we stay firmly on the ground.
Just How Fast Are We Going?
Earth turns once on its axis about every 23 hours and 56 minutes. Because the planet is so big, the ground at the equator has to cover a lot of distance in that time. It moves at roughly 1,040 miles per hour.
Why not a full 24 hours? Because Earth is also traveling around the Sun, it has to turn a little more than once before the Sun comes back to the same spot in the sky. Those extra few minutes make up our familiar 24-hour day.
The farther you are from the equator, the slower you go. At 45 degrees latitude, which runs across the northern United States, the speed drops to about 736 miles per hour. At the North and South Poles, you'd simply turn in place, with a speed of essentially zero.
Fast, but Gentle
The secret is that while we're moving fast, we're turning very slowly. One full turn takes nearly a whole day. A merry-go-round might spin you around every few seconds, which creates a strong outward push. Earth's slow, steady rotation creates only a tiny one.
Physicists call that outward push the centrifugal force. Because Earth rotates so slowly, it's small enough that in everyday life it can usually be ignored. Even in precise scientific work, it's often just folded into what we call local gravity.
Gravity Does the Heavy Lifting
Near the surface, Earth's gravity speeds up a falling object by about 32 feet per second, every second. That's a strong, constant pull toward the center of the planet, and it's what keeps our feet, our oceans, and our air in place.
Gravity isn't exactly the same everywhere, though. It varies by about 0.7 percent across Earth's surface, from its weakest on Nevado Huascarán, a mountain in Peru, to its strongest at the surface of the Arctic Ocean. Among big cities, it's a bit weaker in places like Mexico City and Singapore than in Oslo or Helsinki.
The Spin Leaves a Mark
Earth's rotation may not toss us off, but it has shaped the planet itself. Earth bulges slightly at the equator, where its diameter is about 27 miles wider than from pole to pole. If you stood at sea level at either pole, you'd be about 13 miles closer to Earth's center than at the equator.
That bulge creates a fun bit of trivia. Measured from Earth's center, the highest point on the planet isn't Mount Everest. It's Mount Chimborazo in Ecuador, which sits near the equator on top of that bulge.
So the next time you feel perfectly still, remember you're actually zooming along at hundreds of miles per hour. Gravity has you covered, and it's been holding on to all of us since long before the first merry-go-round.
