What is a Free-Body Diagram (FBD) and what is it used for?

What is a Free-Body Diagram (FBD) and what is it used for?

• A. Isolates the entire system and shows all internal forces.
• B. Shows gravity acting on all objects.
• C. Represents motion using arrows without forces.
• D. Isolates a single object and shows all external forces acting on it.

Answer: (D)

A Free-Body Diagram isolates a single object and shows all external forces acting on it. This setup lets you apply Newton’s laws by summing the external forces with vectors drawn on the object and equating them to mass times acceleration. It focuses on the forces that touch or pull on that object—gravity, normal forces, friction, tension, applied pushes or pulls, etc.—so you can solve for unknowns like acceleration or force magnitudes. This description is the best fit because it emphasizes isolating one object and listing only the external forces acting on it, which is the essence of how FBDs are used. The other statements aren’t accurate: internal forces within a system aren’t shown on a single-object diagram; gravity on every object isn’t what a FBD is defined to depict; and a diagram that shows motion arrows without forces describes velocity or acceleration, not forces.

A Free-Body Diagram isolates a single object and shows all external forces acting on it. This setup lets you apply Newton’s laws by summing the external forces with vectors drawn on the object and equating them to mass times acceleration. It focuses on the forces that touch or pull on that object—gravity, normal forces, friction, tension, applied pushes or pulls, etc.—so you can solve for unknowns like acceleration or force magnitudes.

This description is the best fit because it emphasizes isolating one object and listing only the external forces acting on it, which is the essence of how FBDs are used. The other statements aren’t accurate: internal forces within a system aren’t shown on a single-object diagram; gravity on every object isn’t what a FBD is defined to depict; and a diagram that shows motion arrows without forces describes velocity or acceleration, not forces.