At one time or another, you've probably been grounded for doing something you weren't supposed to be doing. Not good! But, that's not exactly the kind of grounding we're talking about today, even though both kinds are about staying put!

The Earth rotates on its axis every day — once every 24 hours. The Earth also flies through space at about 67,000 miles per hour as it travels around the Sun. And yet you're able to stand still with your feet planted firmly on the ground. Have you ever wondered why you don't simply fly off into space?

You can thank gravity for the fact that you're firmly grounded on the Earth. When you consider the alternative, being grounded by gravity isn't so bad, is it?

But what exactly is gravity? Believe it or not, it's still a bit of a mystery. Scientists from Isaac Newton to Albert Einstein have studied it and come up with different theories to explain it. However, exactly how gravity works still cannot be fully explained.

So what do we know about gravity? We know that gravity is an invisible force that attracts all objects towards each other. It has been around since the beginning of the universe, and it works the same way everywhere in the universe on all kinds of objects of all different sizes.

We know that gravity keeps the Moon in orbit around the Earth. It also holds the planets in orbit around the Sun. Most importantly to you, it's what keeps you on the ground and causes objects to fall toward the Earth.

Isaac Newton first described gravity as a force. Later, Albert Einstein theorized that gravity is a result of the curvature of space and time. Sound complicated? It is! And no one truly understands WHY gravity works. However, we can see its results and learn some things about it.

Scientists have learned that anything that has mass also has a gravitational pull. The more massive an object is, the stronger its gravitational pull will be. Also, the closer you are to an object, the stronger its gravitational pull will be on you.

For example, large, heavy objects, like airplanes, need lots of power to counteract gravity. That's why airplanes have such large engines.

Likewise, astronauts who have traveled to the Moon have experienced the feeling of weighing less on the Moon. This is the result of the Moon being less massive than the Earth. As a result, its pull on a human being is much less than that of the Earth.

When in space, astronauts may also experience the feeling of being weightless. You've probably seen pictures of astronauts and objects floating inside of space vehicles. Is this because there is no gravity in space? Absolutely not!

There is gravity everywhere. However, the farther from the Earth that the astronauts get, the weaker the gravitational pull on them will be. It never gets to zero, but it can get too small to matter. As a result of extremely weak gravitational forces acting in space, the astronauts can float around inside their space vehicles!

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May tomorrow’s Wonder of the Day rise up to meet you!