EM 274: Notes on 2-D Free Body Diagram Sketches

  1. Label all forces/couples, or indicate values if known
  2. Label all body geometry (distances and angles), or indicate values if known
  3. Support mechanisms should not be part of the sketch, only the forces or moments they exert
  4. Show coordinate axis sytem
  5. centered to make solution process simplest, normally at a constraint point
  6. aligned to make solution process simplest, normally one axis connecting constraint points
  7. not necessarily the same axis used in sytem diagram
  8. Check for adequate contraints
  9. body is prevented from moving or rotating
  10. reactions are not all concurrent
  11. Check FBD is not over-constrained
    (i.e. statically determinate, no redundant constraints)
  12. can any constraint(s) be removed and FB still be adequately constrained?
  13. if the direction of a force is known at a support point show a single force in its proper direction and a value for the angle
  14. if the magnitude of a force is known at a support point show its value on the vector and label the unknown angle
  15. for either of the two previous cases do not show cartesian components; this will make the body appear to be over-constrained
  16. Draw a separate FBD for each partthat is not rigidly connected to othe