When the net force acting on an object is zero meaning all forces acting upon it are balanced the object experiences no change in its velocity. This state of zero net force results in zero acceleration. For example, a book resting on a table experiences the downward force of gravity and the upward supporting force from the table. These forces are equal in magnitude and opposite in direction, resulting in a net force of zero and therefore no acceleration.
This principle, a cornerstone of Newtonian mechanics, is fundamental to understanding motion and equilibrium. It explains why stationary objects remain at rest and why moving objects continue at a constant velocity unless acted upon by an unbalanced force. Historically, understanding balanced forces was crucial for advancements in engineering, architecture, and even astronomy, allowing for predictions of planetary motion and the design of stable structures.