Lecture on Free Body Diagrams

Introduction to Free Body Diagrams

• A Free Body Diagram (FBD) represents all the forces acting on an object.
• Important to consider the direction and magnitude of each force.
• Forces are represented with arrows; the size of the arrow represents the magnitude.

Situation 1: Box on a Table at Rest

• Object: A box on a table
• Forces Involved:
  • Gravitational Force: Downward
  • Normal Force: Upward, equal in magnitude to gravitational force
• Key Point:
  • Forces are balanced (equal and opposite), resulting in no movement.
  • Net force = 0

Situation 2: Box with Rightward Acceleration

• Object: Box moving across a table
• Forces Involved:
  • Gravitational Force: Downward
  • Normal Force: Upward
  • Applied Force: Rightward, large magnitude
  • Frictional Force: Leftward, small magnitude
• Key Point:
  • Unbalanced forces due to rightward acceleration.
  • Net force is not zero; rightward applied force is greater than frictional force.

Situation 3: Box at Constant Velocity

• Object: Box moving right at constant velocity
• Forces Involved:
  • Gravitational Force: Downward
  • Normal Force: Upward
  • Applied Force: Rightward, equal in magnitude to frictional force
  • Frictional Force: Leftward, equal in magnitude to applied force
• Key Point:
  • Forces are balanced (net force = 0), thus maintains constant velocity.

Situation 4: Skydiver at Constant Velocity

• Object: Skydiver
• Forces Involved:
  • Gravitational Force: Downward
  • Air Resistance: Upward
• Key Point:
  • Forces are balanced; hence, the skydiver falls at constant velocity.
  • No normal force or applied force.

Situation 5: Skydiver in Free Fall

• Object: Skydiver
• Forces Involved:
  • Gravitational Force: Downward
  • Air Resistance: Upward, lesser magnitude versus gravitational force
• Key Point:
  • Unbalanced forces due to free-fall acceleration.
  • Gravitational force is greater than air resistance, causing acceleration.

Conclusion

• Understanding forces and their representations in FBDs is crucial for analyzing motion.
• Concepts like balanced and unbalanced forces explain static and dynamic scenarios.
• Encourages further exploration through additional resources.