You're very close! The First Law of Motion, also known as Newton's Law of Inertia, has a slightly different wording. Here's the correct statement:

An object at rest stays at rest, and an object in motion stays in motion at a constant velocity unless acted upon by a net external force.

Here's the breakdown:

* Inertia: This is the tendency of an object to resist changes in its motion. Objects naturally want to stay in their current state of rest or motion.

* Net Force: This is the overall force acting on an object. If the net force is zero, the object will maintain its state of motion.

* Constant Velocity: This means moving at a constant speed in a straight line.

So, while your statement captures the essence of inertia, it misses the crucial point about the *net* external force and *constant velocity* for objects in motion.