Here's why:
* Newton's First Law of Motion states that 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.
* Balanced forces mean that the forces acting on an object cancel each other out. There's no net force acting on the object.
* Constant velocity means the object is either at rest (zero velocity) or moving at a constant speed in a straight line.
Example:
Imagine a book sitting on a table. The force of gravity is pulling the book down, but the table is pushing back up with an equal and opposite force. These forces are balanced, so the book remains at rest (constant velocity of zero).
