## alffer1 one year ago Hey all! In the following problem I need to draw the free-body diagram of the cylinder an determine the magnitudes of AC and CD: The hydraulic cylinder is subjected to three forces. An 8 kN force is exerted on the cylinder at B that is parallel to the cylinder and points from B toward C. The link AC exerts a force at C that is parallel to the line from A to C. The link CD exerts a force at C that is parallel to the line from C to D. I'll include the image in the comments.

1. alffer1

Here is a rough sketch of the problem, with included dimensions.

2. alffer1

I need the free body diagram. I can figure it out from there.

3. LastDayWork

Attempt to draw it yourself first; and I'll correct it :)

4. alffer1

Ok here is what I got, but it makes no sense to me. There must be normal forces somewhere but I'm not sure where to put them:

5. LastDayWork

I think the three forces are themselves normal forces (or tension; whatever you are used to call them).

6. alffer1

Wait wha........but i'm still missing forces in order to balance aren't I? as it is now point C should be moving upward. There must be some force keeping it down right?

7. LastDayWork

Honestly, I don't know how this arrangement will work (or what purpose it is used for). As we are using rods (instead of strings), the tension will change its direction from compressional to extensional (or vice-versa) to keep the point C in equilibrium.

8. LastDayWork

Consider posting the original question.

9. alffer1

This question is coming out of my textbook so I'm not sure how to get it from the page to here.

10. LastDayWork

If you have a camera, upload the image.

11. alffer1

ok in proceso.

12. alffer1

Ok I got it:

13. LastDayWork

@Mashy

14. LastDayWork

@Vincent-Lyon.Fr @douglaswinslowcooper @Garm

15. LastDayWork

@UnkleRhaukus

16. LastDayWork

Took some time, but I think I understand it now. (Note that the arrows indicate force vectors.) Try to find how I chose between compressional and extensional tension? Also, find where does Fex comes from?

17. LastDayWork

^^ @alffer1

18. alffer1

ok yeah I'm looking at it now. I understand where everything is coming from except the Fex. the problem doesn't say anything about an external force being applied...

19. LastDayWork

It's not an external force; take a closer look at the diagram.

20. LastDayWork

I used the term Fex in the same sense as "...Cats are liquid" :D

21. alffer1

ok let me see if I understand the diagram: the forces in each of the rods causes a reaction force at the other points. The liquid in the cylinder is compressed causing a reaction force from the liquid?

22. LastDayWork

There is also a string attached to the hydraulic cylinder. The hydraulic part only involves the fact that we can convert a weaker force into a stronger one; simply by changing the area on which the force is applied.

23. alffer1

OHHH so the tension in the string pulling backwards is what is causing Fex? and it's equal and opposite to the 8000 N force?

24. LastDayWork

For more on hydraulics; read - http://en.wikipedia.org/wiki/Hydraulic_drive_system. "...OHHH so the tension in the string pulling backwards is what is causing Fex?..." Yes "...it's equal and opposite to the 8000 N force?..." You can do the (vector) addition yourself as I am a very lazy guy :D

25. alffer1

ok awesome this actually makes sense now. just needed to figure that out.

26. alffer1

Could you take a look at one quick question?

27. LastDayWork