ELI5: What is orbit?

Imagine you're swirling a ball tied to a string around your head. That ball is like a planet, and your head is like a star (like our Sun!). The string keeps the ball from flying away. That swirling is kind of like an orbit.

Why doesn't the ball just crash into your head, or fly off into the distance? It's because you're pulling on the string, and the ball is moving sideways really fast.

• Your pulling is like gravity. Gravity is a force that pulls things together. The bigger something is, the stronger its gravity. The Sun is huge, so it has a lot of gravity.
• The ball's sideways movement is like the planet's speed. Planets are moving very, very fast!

Think about riding a bike. If you stop pedaling, you slow down and eventually fall over. But if you keep pedaling, you stay upright and move forward. Planets are always "pedaling" (moving sideways), so they never fall into the Sun.

Different planets have different orbits because they are different distances from the Sun and have different speeds. Some are closer and faster, some are further and slower. But they're all constantly "falling" around the Sun, like that ball on a string!