* Newton's First Law of Motion: An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

* No Friction: In frictionless space, there's no air resistance or any other force to slow the cannonball down.

* Inertia: The cannonball possesses inertia, which is its resistance to changes in motion. Once in motion, it will continue moving in a straight line at a constant speed without any external force.

Important Note: This is a theoretical scenario. In reality, even in space, there are some forces acting on objects, like gravity and the occasional dust particle or gas molecule. However, the effect of these forces is much smaller than what you'd experience on Earth.