* Newton's First Law of Motion (Inertia): 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.
* Zero Net Force: This means all the forces acting on the object are balanced. They cancel each other out.
Examples:
* A car moving at a constant speed on a straight road: The engine force propelling the car forward is balanced by friction and air resistance.
* A ball rolling across a smooth, frictionless surface: Once the ball is given an initial push, there is no net force to slow it down, so it continues moving at a constant speed.
Key Point: The net force determines if an object's motion *changes*, not necessarily if it's in motion at all.
