Lecture on Free Body Diagrams

Introduction to Free Body Diagrams (FBD)

• A Free Body Diagram (FBD) is essential for problems involving forces.
• Definition: A diagram showing all forces acting on an isolated object.
• Also known as a force diagram.

Drawing a Free Body Diagram

1. Start: Draw a simple picture of the object and its surroundings.
2. Center of Mass:
   • Represented by a dot in the middle of the object.
   • For constant mass density objects, it is at the center.
   • More detailed definition will be covered in future lessons.

Forces Acting on an Object

1. Gravity:

   • Force of Gravity (Weight): Mass times acceleration due to gravity, directed straight down.

2. Normal Force (Fₙ):

   • Acts perpendicular (normal) to a surface.
   • Always a push, not a pull.
   • Balances the force of gravity in this context.

3. Arrows in FBD:

   • Represent force vectors.
   • Length corresponds to magnitude.
   • Equal length arrows indicate equal magnitude of forces.

Changing Free Body Diagram

1. Applied Force (Fₐ):

   • Force exerted by a person or object on another object.

2. Frictional Force (Fₙ):

   • Definition: A force that opposes motion.
   • Acts parallel to the surface, preventing motion.

Free Body Diagram on an Incline

1. Forces:

   • Gravity: Always directed straight down.
   • Normal Force: Perpendicular to the incline.

2. Force of Friction:

   • Prevents sliding down the incline.
   • Acts up and parallel to the incline.

Key Takeaways

• Free Body Diagrams are crucial for understanding forces in physics problems.
• A complete FBD must account for all forces to accurately predict motion.
• Regular practice with FBDs will improve understanding of force interactions.