Jump as high as you can and you will realise something is pulling you back toward the ground. You cannot see it, touch it, or hear it, but it is always there. An invisible force called gravity. It’s one of the most important forces in our universe. Gravity keeps our feet on the ground, makes rain fall from the sky, and even holds the Moon as it travels around Earth. Get ready to explore the amazing force that keeps everything from floating away.

In the 1600s, an English scientist named Isaac Newton began studying the mysterious force that pulled objects downward. One story says that Newton saw an apple fall from a tree. He wondered why the apple fell straight down instead of floating away. His questions led him to an amazing idea: Earth pulls objects toward itself for some reason. Newton discovered that gravity is not just something that makes apples fall but it is a force that reaches every corner of the universe.

Everything that has mass has gravity. The more mass something has, the more gravity it has. Gravity does more than keep your feet on the ground, it also determines how much an object weighs. Imagine you weigh 100 pounds on Earth. On the Moon you would weigh only about 16 pounds! Talk about instant weight loss! This happens because the Moon has much weaker gravity than Earth. You are the same person and you still have the same amount of matter, or mass, but your weight would change because the Moon’s gravity is not as strong.

Gravity doesn’t stop here. It has a huge influence on planets, moons, and spacecraft and has an important role in space flight. When a spacecraft launches, it has to go fast enough to escape the Earth’s strong pull. This is called the escape velocity. A rocket has to be going at least 25,000 miles per hour to escape the Earth’s gravitational pull? Once the rocket has escaped the gravitational pull it’s still pulled toward the ground but at a lower rate. This is called Microgravity. Micro means very small. Microgravity is what is going on when you see astronauts floating around with their hair standing straight up. Astronauts feel weightless because they and their spacecraft are constantly falling around Earth. They keep missing the ground, so they stay in orbit.

Have you ever balanced a pencil on your finger and moved it back and forth until you found the perfect spot where it would stay balanced? That spot is connected to an object’s center of gravity, the point where its weight is balanced. Now imagine trying the same trick with a hammer. Because a hammer has a heavy metal head on one end and a lighter handle on the other, its center of gravity is closer to the heavy end. You would have to find a different spot to balance it! The same idea works with objects all around us. Gravity is always pulling on every part of an object, and the center of gravity helps us understand where all those pulls balance out.