Free body diagram and force vectors

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SUMMARY

The discussion focuses on the analysis of a free body diagram (FBD) for a system involving a cylinder and two rods (CD and CE) connected at point C. Participants emphasize the importance of correctly identifying the body for which the FBD is drawn, noting that internal forces, such as tension, should not be included in the FBD of the body experiencing those forces. The symmetry of the system simplifies the analysis, allowing for a more straightforward approach to decomposing force vectors in terms of angles and weights.

PREREQUISITES
  • Understanding of free body diagrams (FBD)
  • Knowledge of force decomposition techniques
  • Familiarity with tension forces in mechanical systems
  • Basic principles of static equilibrium
NEXT STEPS
  • Study the principles of static equilibrium in mechanical systems
  • Learn how to construct free body diagrams for complex structures
  • Explore methods for decomposing forces into components
  • Investigate the role of tension in multi-body systems
USEFUL FOR

Students of physics and engineering, mechanical engineers, and anyone involved in analyzing forces in static systems will benefit from this discussion.

samjohnny
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Homework Statement



Attached, where AC=BC=2R and CD=CE=3R. I need to work out the force the cylinder exerts on the cross section (in order to work out the moment at C). So first I'm trying to work out the free body diagrams for this system. Is it as I've attached? How do I draw the tension vector? And then I'm having a hard time defining and decomposing the force vectors in terms of theta, mg etc. Can anyone lend a hand?
 

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hi samjohnny! :smile:

we need to know a little more …

are CD and CE hinged at C?​
samjohnny said:
So first I'm trying to work out the free body diagrams for this system. Is it as I've attached? How do I draw the tension vector?

it would be easier to start with the free body diagram of the cylinder

your puzzlement as to how to draw the tension is caused by choosing the wrong body

a free body diagram shows all the external forces on a body, so it won't show up on a body for which it's an internal force!

you need to do it for one rod :wink:

(the symmetry makes that a lot easier than it would otherwise be)
 
tiny-tim said:
hi samjohnny! :smile:

we need to know a little more …

are CD and CE hinged at C?​
it would be easier to start with the free body diagram of the cylinder

your puzzlement as to how to draw the tension is caused by choosing the wrong body

a free body diagram shows all the external forces on a body, so it won't show up on a body for which it's an internal force!

you need to do it for one rod :wink:

(the symmetry makes that a lot easier than it would otherwise be)

Hey! Thanks for the reply.

Yeah they're connected at C. Cool, I see what you mean. I'll take another crack at it.
 

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