* Gravity: The primary force keeping planets in their orbits is the gravitational attraction between the planet and its star. The star's massive size creates a strong gravitational pull that keeps the planet in a curved path around it.

* Inertia: Planets are constantly moving forward, a property called inertia. Imagine a ball on a string being swung in a circle. The ball wants to continue moving in a straight line, but the string pulls it back towards the center, making it move in a circle. This is similar to how a planet's inertia wants to make it fly off into space, but gravity from the star pulls it back in, keeping it in its orbit.

Think of it like a delicate balance:

* Gravity: The "string" pulling the planet towards the star.

* Inertia: The "ball's" tendency to move in a straight line.

Together, these forces create a stable orbit around the star.