Today’s Wonder of the Day was inspired by Erin from PA. Erin Wonders, “Why can't we feel the earth spin?” Thanks for WONDERing with us, Erin!

Have you ever had a picnic in your backyard? On a sunny day, it's fun to spread a blanket out on the ground. After you munch on chips and sandwiches, you can take a little siesta on the blanket.

Before your eyes close, you might enjoy staring up at the sky. With your back against the solid ground and your eyes on the clouds above, you can contemplate what a miraculous world we live in and on.

Even though Earth feels solid beneath us and it might seem like we're motionless, we're actually on a giant sphere of rock, dirt, and water that's constantly spinning around at the same time that it's hurtling through space around the Sun. We know this constant motion takes place, yet we do not feel it. Why is that?

Are our human senses not finely-tuned enough to detect the rotation of Earth? Perhaps Earth doesn't rotate fast enough to be felt by humans, who are tiny in comparison to Earth?

Earth definitely rotates fast enough for humans to feel. Our senses can detect very subtle changes. So what's going on? It's science at work! There are several reasons we don't feel Earth's rotation.

Everything in the universe spins…planets, stars, and even entire galaxies! As Earth formed out of a cloud of gas and dust, gravity pulled everything together.

Kind of like water swirls down a drain, all that matter began to spin as it compressed into the ball we know today as Earth. Scientists would tell you that the scientific principle at work causing the spin is known as the conservation of angular momentum.

How fast does Earth spin? Let's calculate it! The distance around Earth, called its circumference, is about 24,000 miles. Earth spins on its axis and completes one full rotation in 24 hours. We can divide 24,000 miles by 24 hours to give us Earth's speed of rotation. Therefore, we can conclude that Earth spins at approximately 1,000 miles per hour (about 1609 kilometers per hour). That's fast!

Have you ever ridden a really fast roller coaster? Roller coasters can travel at 100 miles per hour or more. If roller coasters are that fast, can you imagine what it would feel like to feel Earth spin at 1,000 miles per hour? Wow! That's hard to imagine, isn't it?

Despite the fast rotation of Earth, we don't feel it. The main reason is because we — along with everything around us, from trees to skyscrapers — are moving right along with Earth. We also don't feel Earth's spin because Earth's motion is very smooth.

When you're traveling in a car on the highway, you're going the same speed as the car. If the ride is smooth, you can read a book and you don't even sense that you're moving. The only time you notice is when the car speeds up, slows down, or rolls over a bumpy patch of road. Since Earth doesn't speed up or slow down like a car on a highway, we never notice its spin!

The next time you gaze up at the clouds or stars, think about how fast Earth is spinning. Since you're moving right along with it and the motion is so smooth, you don't feel a thing!

Wonder What's Next?

You don’t have to be Superman to appreciate the strength of the material at the heart of tomorrow’s Wonder of the Day!