Kinematics and Dynamics F. Newton's Laws of Motion Key Concepts Inertia is the property of an object that resists changes in its state of rest or motion. Inertia depends on mass. Mass is a measure of the inertia of an object. Galileo challenged Aristotelian notions about motion by performing experiments. A net force is the resultant of all forces acting on an object.
Equilibrium exists if the net force is zero.
An unbalanced force exists when the resultant of all of the forces acting on an object does not equal zero. If all of the forces acting on an object cancel one another, the resultant vector is zero and no unbalanced force exists. The object is in equilibrium. An object at rest on a table has its weight opposed by a normal force acting on the object by the table. The net force is zero.