Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Is this real? 3

Status
Not open for further replies.
Sort by date Sort by votes
Well, I can't find it anywhere but I am sure this was discussed in the past as the Devil's Hook or some such...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand
 
Upvote 0 Downvote
There is no need for the horizontal friction at the top for this to be stable.
 
Upvote 0 Downvote
The friction is along the string on contact surface, the match provides pivot point.
 
Upvote 0 Downvote
Friction is absolutely not necessary; the Devil's Hook cited above uses no friction. If you carefully look at the belt, its profile isn't horrifically different than that of the cord in the video.

Likewise, Megastucture's figures require zero friction; stability is guaranteed by moving the CG inboard of the pivot point on the edge.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
Upvote 0 Downvote
Friction is absolutely not necessary;
Click to expand...

I wouldn't be so sure. Who can write equilibrium equations for this system, say the hanging weight >= weight of string?

image_v43mbg.png
 
Upvote 0 Downvote
That's not the same mechanism @retired13. The compression strut is required to create a force couple. Also, the load under the table is resisted vertically by contact between the match and table. In your figure you provide no vertical, or lateral, restraint, which of course creates a system that cannot be in equilibrium.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”
 
Upvote 0 Downvote
retired13_edit_wz4jge.png


“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”
 
Upvote 0 Downvote
Mega,

Very good. How about this now?

image_b8mpkx.png
 
Upvote 0 Downvote
So what's supporting the pulley and the pin? This is a completely different mechanism than what is being discussed.
 
Upvote 0 Downvote
Assume the pulley and pin have out of page supports that can take vertical load. The concept is the same.
 
Upvote 0 Downvote
The concept is not remotely the same!

In the video, the match at the top is taking the load through shear. Your sketch has a fabric string that will not be able to take shear.
 
Upvote 0 Downvote
You didn't think hard enough :)
 
Upvote 0 Downvote
Friction and compression are all that hold joints at matches and string together. The free body diagrams are simple.
 
Upvote 0 Downvote
@retired13
Your drawing bears zero resemblance to the problem described, since there is no W2 anywhere in the problem, other than the weight that held the match in place, initially. By your drawing, removal of the weight would immediately result in everything falling, and there cannot possibly enough friction to keep the string (match) from sliding off the table. You are solving some other problem of your own creation.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
Upvote 0 Downvote
IR,

See Composite' response. I am amused that a chemical engineer knows structural tricks.
 
Upvote 0 Downvote
I can't believe this thread is still going. Isn't this something we played around with as kids? Alternatively if you are still confused it isn't too hard to do it yourself.
 
Upvote 0 Downvote
human909 said:
I can't believe this thread is still going. Isn't this something we played around with as kids? Alternatively if you are still confused it isn't too hard to do it yourself.
Click to expand...

Shows why many of us chose engineering. Or did it choose us?
 
Upvote 0 Downvote
It isn't difficult to prove that the problem is statically stable.. if my calculations are right, zero (or nearly close to zero) horizontal reaction and overturning moment is produced at the support.
Screenshot_20200914_181211_zojunn.jpg
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

bhiggins
  • Question Question
Is this structure braced?
Replies
5
Views
964
bhiggins
bhiggins
BridgeEngineer21
  • Question Question
External anchorage of reinforcement - is this feasible?
2
Replies
37
Views
17K
Retrograde
Retrograde
Pretty Girl
  • Question Question
What is this Rm line in this biaxial interaction chart - Eurocode 2
Replies
7
Views
1K
Pretty Girl
Pretty Girl
P
  • Locked
  • Question Question
What category of crack is this?
Replies
7
Views
2K
JAE
JAE
rpand4
  • Question Question
Learning Structural Connection Types – Pin vs Fixed (Real World Example)
Replies
13
Views
8K
Ron247
Ron247

Part and Inventory Search

Sponsor

Back
Top