Lecture Notes: Force Diagrams and Free Body Diagrams

Introduction

• Topic: Understanding force diagrams and free body diagrams using a box on a table.
• Key concept: Forces acting on an object (e.g., a box on a table).

Forces Acting on the Box

• Gravity (F_g or Weight (W))
  • Acts downward due to Earth's attraction.
  • If the table wasn't there, the box would fall due to gravity.
• Normal Force
  • Acts upward exerted by the table to keep the box up.

Types of Diagrams

Force Diagrams

• Draw the object and depict forces with arrows.
• Gravity usually depicted from the center of the object.
• Normal force shown as upward arrow.
• Always label forces and add a key.

Free Body Diagrams

• Simplified depiction using a dot.
• All force arrows point away from the dot.
• Only one of F_g or W needed.
• No need to draw the table, only the object.
• Adding a key is beneficial to show understanding.

Example: Box with Applied Force and Friction

• Applied Force (F_a): Force exerted by a person pushing the box.
• Friction (F_f): Opposes the movement caused by imperfections (or teeth) on surfaces.
• Gravity & Normal Force: Act as described above.

Depictions

• Force Diagram:
  • Applied force and friction shown with arrows.
  • Variations in depiction methods are fine as long as the concept is understood.
• Free Body Diagram:
  • Arrows always point away from the dot.
  • Easier than force diagrams as it doesn't require drawing the object.

Conclusion

• Focus on mastering free body diagrams as they are more commonly used.
• Adapt to the teacher’s method if it differs, but ensure understanding of concepts.

• Note: Practice frequently as each teacher might have a unique approach; understanding the underlying principles is crucial.