if resultant force acting on object = 0, we say forces acting on object are balanced.
| Table exerts an upward force F (normal force) that pushes on the book F = W (weight of the book)  - 2 forces acting on book are equal ⇒ act in opposite directions. - thus, resultant force = 0 and the book remains stationary. - Book is at rest ⇒ acceleration = 0 | Force F is applied on a book ⇒ and it moves in a straight line across a rough table. F = F (frictional force between book and table)  - resultant force ⇒ acting on book are equal ⇒ but act in opposite directions - Resultant force = 0 ⇒ book continues moving at constant velocity. |
Law
Newtons first law of motion states that every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it. #PhysicsDefinitions