Primary source

Have you ever wondered why, when you jump up, you always come back down. Or why your favorite toy doesn't just float away into the sky. It feels like something is holding you, a gentle but strong hug that keeps your feet planted on the grass and your bed in your room. It’s an invisible secret, a superpower that the whole world shares. You can feel me when you drop a crayon and it lands on the floor, or when you pour juice and it goes right into your cup. This constant, gentle pull is with you every second of every day, keeping everything in its place. That special, invisible hug is me. I am Gravity.

For a very, very long time, people could feel me but they didn't have a name for me. They just knew that things fell down, not up. Then, one day, a very curious man was sitting outside, thinking about the universe. His name was Isaac Newton, and he loved to ask questions about everything. Around the year 1666, as he sat under an apple tree, he saw an apple let go of its branch and fall straight to the ground. Plop. He started to wonder why the apple fell down and not sideways, or even up. That little apple gave him a gigantic idea. He realized that the Earth was pulling on the apple, just like it pulls on you and me. He understood that bigger things have a bigger pull, and our huge Earth has a very strong pull. This is my secret power. Isaac Newton was so excited that he wrote down all his ideas to share with everyone, explaining that I am the force that not only makes apples fall but also keeps the Moon from floating away into space. He shared his wonderful discoveries in a very important book on July 5th, 1687.

My job is much bigger than just making sure apples fall. I am the reason the beautiful planets, like Mars and Jupiter, do a slow and steady dance around the Sun. Without me, they would all zoom off in different directions. I also help right here on Earth. I pull the rain from the clouds down to the ground, giving all the plants and flowers a nice drink so they can grow big and strong. When you go down a slide at the playground or swing back and forth on a swing set, that’s me helping you have fun. Many years after Isaac Newton, another super smart person named Albert Einstein came up with even more amazing ideas about how I work, showing that there’s always something new to discover. So, while you're playing, remember that I am here, holding the whole universe together and keeping you safe and sound on our wonderful planet.