Overview
This lecture introduces the concepts of force diagrams and free body diagrams, illustrating how forces act on objects like boxes on a table or being pushed across a surface.
Forces Acting on an Object
- Gravity (force of the Earth) pulls objects downward; represented as ( F_g ) or weight (( W )).
- The surface (like a table) pushes up with a normal force to support the object.
- If only gravity acts, the object falls; the normal force prevents this.
Force Diagrams vs. Free Body Diagrams
- Force Diagram: Draw the object (e.g., a box), then show forces as arrows from the center and label them.
- Free Body Diagram (FBD): Draw a simple dot to represent the object; all force arrows point away from this point and are labeled.
- Only choose one label for gravity (( F_g ) or ( W )); consistency is key.
- Include a key or legend to explain symbols in both diagram types.
Additional Forces When Pushing an Object
- An applied force (( F_a )) pushes the object.
- Friction (( F_f )), caused by microscopic surface imperfections, resists movement.
- Gravity and normal force still act vertically on the object.
Drawing Diagram Guidelines
- In FBDs, arrows must always point away from the object (dot).
- Force diagrams show the object, but not the supporting surface.
- Use consistent labeling, and clarify arrows and forces with a legend.
Key Terms & Definitions
- Gravity (( F_g )) — The attractive force pulling objects toward the Earth.
- Weight (( W )) — The gravitational force acting on an object.
- Normal Force (( F_N )) — The perpendicular force a surface exerts to support an object.
- Friction (( F_f )) — The resisting force due to surface imperfections.
- Force Diagram — A diagram showing the object with arrows for all acting forces.
- Free Body Diagram (FBD) — A simplified diagram using a dot and arrows for all forces acting on the object.
Action Items / Next Steps
- Practice drawing both force diagrams and free body diagrams for simple objects.
- Review how to label and describe forces acting on stationary and moving objects.