Lecture on Forces and Diagrams

Introduction to Forces on a Box

• Scenario: A box resting on a table.
• Forces Acting on the Box:
  • Gravity (Fg or W): Force of Earth attracting the box; also referred to as weight.
  • Normal Force: The force exerted by the table to keep the box up.

Types of Diagrams

1. Force Diagrams

• Description: Draw the object with arrows indicating forces.
• Key Points:
  • Gravity is represented with an arrow from the center of the object.
  • Normal force is shown with an arrow pointing upwards.
  • Always label the forces clearly.
  • Add a key to make it neat and understandable.

2. Free Body Diagrams

• Description: Simplified representation with a dot and arrows.
• Key Points:
  • Arrows point away from the dot.
  • Choose one label for gravity, either Fg or W.
  • No need to draw the object, just the forces.
  • Add a key for clarity.

Example with Additional Force

• Scenario: A person pushing a box.
• Additional Forces:
  • Applied Force (Fa): Pushing force by a person.
  • Friction (Ff): Opposes the motion due to surface imperfections.

Understanding Friction

• Microscopic View: Surfaces have imperfections that cause friction.
• Effect: Prevents box from sliding continuously without force.

Constructing Diagrams for Example

Force Diagram

• Components:
  • Applied force (Fa), shown with an arrow in the direction of the push.
  • Friction (Ff), shown opposing the motion.
  • Normal and gravitational forces as before.

Free Body Diagram

• Key Points:
  • Arrows point away from the object.
  • Avoid arrows pointing towards the object even for applied forces.

Conclusion

• Free Body Diagrams are more popular and important to understand.
• Adapt to the methods preferred by your teacher.
• Emphasize understanding the concept over memorizing techniques.
• Practice is key to mastering the diagrams.

• Tip: Always label your diagrams and include a key for clarity.