Gravity and the Solar System: What Keeps Worlds in Orbit

Hi, I'm Lumi! Let's talk about gravity, the invisible force that ties our whole solar system together. Gravity is an attractive force, which means it always pulls things toward each other, never pushes them apart. Every object that has mass has gravity. You have it, this planet has it, and the Sun has it. Two things change how strong that pull is. First is mass: more mass means a stronger pull, which is why the giant Sun pulls far harder than a tiny moon. Second is distance: the closer two objects are, the stronger the pull, and as they move farther apart the pull gets weaker. So why don't the planets just fall straight into the Sun? Each planet is also moving sideways, very fast. A planet keeps moving sideways because of its inertia: objects in motion stay in motion unless a force stops them. The Sun's gravity keeps bending that straight-line motion into a curve, again and again, so the planet keeps looping around instead of crashing in. That curving path is an orbit. Moons orbit planets the same way, held by the planet's gravity. Because gravity follows these steady rules, the solar system is gravitationally bound and predictable. Astronomers can calculate exactly where a planet will be years from now. If anything feels tricky, try the prediction activity below, then test yourself with the questions.