Gravity and Orbits: What Holds the Solar System Together

Hi, I'm Lumi! Let's figure out what keeps the whole solar system from drifting apart. Gravity is a pulling force — and here's the key idea: every object that has mass pulls on every other object, even across completely empty space, with no connection between them. There is no rope, wire, or beam involved. The Sun pulls on Earth from 150 million kilometers away, through nothing at all. This is called action at a distance, and it surprised scientists too when they first discovered it. Two things set how strong gravity is. First, mass: the more mass an object has, the stronger it pulls. The Sun has enormous mass, so it tugs on every planet. Second, distance: the farther apart two objects are, the weaker the pull becomes. A planet close to the Sun feels a stronger pull than one far away. So why don't planets fall straight into the Sun? Because they are moving sideways, very fast. Imagine throwing a ball forward. Gravity curves its path downward and it hits the ground. Now throw it so fast that the ground curves away beneath it just as fast as it falls — the ball keeps curving but never lands. That continuous, curving fall is an orbit. If a planet moves too slowly, gravity wins and pulls it inward. If it moves too fast, it escapes into space. A stable orbit is the balance point. Remember: speed across + pull inward = loop. You can picture that in words without needing any diagram. (The swinging-ball animation in the lesson viewer also shows this if it is available to you.)