Understanding Forces and Free Body Diagrams
Forces are pushes or pulls that cause objects to accelerate. Several common forces affect objects in our daily lives. An applied force is what we create when we physically push or pull an object. The normal force acts perpendicular to a surface, pushing back when objects press against it. Frictional force opposes motion between surfaces in contact, while tension force is the pulling force transmitted through a string, rope, or cable.
Free Body Diagrams (FBDs) are visual tools that show all forces acting on an object. These diagrams help us see when forces cancel each other out or when they combine to create a net force. Remember, according to Newton's laws, an object accelerates only when there's a net force acting on it.
When drawing an FBD for a book resting on a table, we include two main forces: the gravitational force pulling down and the normal force pushing up. Since the book isn't moving, these forces must be equal in magnitude but opposite in direction, resulting in zero net force.
💡 When forces are balanced (equal and opposite), the net force is zero and the object won't accelerate—it will either remain at rest or continue moving at constant speed in a straight line.
