Force couple supported by line

  • Context: Undergrad 
  • Thread starter Thread starter teleswamp
  • Start date Start date
  • Tags Tags
    Couple Force Line
Click For Summary

Discussion Overview

The discussion revolves around calculating the force distribution along a line support for a force couple, particularly in the context of a block supported at two points. Participants explore the implications of different support types and the conditions for equilibrium.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks clarification on how to determine the force distribution along a line support for a force couple.
  • Another participant asserts that the initial analysis is incorrect, stating that the block is not in equilibrium and questions the assumptions about weight and horizontal reactions.
  • A participant suggests simplifying the problem by assuming the block is weightless and provides specific values for horizontal and vertical reactions at the supports.
  • There is a challenge to the correctness of the proposed reactions, emphasizing the need for proper analysis to arrive at accurate results.
  • One participant describes the support configuration as having a pin connection on one end and a roller on the other, providing specific reaction values for both supports.
  • Another participant corrects the vertical and horizontal reaction values, indicating a need for clarity in the support conditions.
  • A later reply explains that having two pinned joints leads to an indeterminate system, suggesting that using a roller allows for solving the vertical reactions through moment conditions.
  • Assumptions about even upward pressure along the line of support are proposed, with a suggestion to replace this pressure with a single force acting through the centroid of the pressure line.

Areas of Agreement / Disagreement

Participants express disagreement regarding the correctness of the initial analyses and assumptions about the support conditions. Multiple competing views on the reactions and equilibrium conditions remain unresolved.

Contextual Notes

Limitations include assumptions about weightlessness, the nature of the supports, and the conditions for equilibrium, which have not been fully resolved.

teleswamp
Messages
4
Reaction score
0
Hi,

I know how to calculate the reaction to a force couple supported by 2 points. But what if it is supported by a line. See example attached. How do I figure the force distribution along the constant support?

Thanks
 

Attachments

Physics news on Phys.org
Good evening teleswamp and welcome to Physics Forums.

Actually neither of your analyses are correct so let us start with the simplest first one and get that correct.

The block as drawn is not in equilibrium so you cannot apply the equations of equilinrium to it.

Firstly does you block have no weight?

Secondly what of the horizontal components of the reactions at the two support points?
 
Last edited:
Yes, for simplicity assume the block is essentially weightless. Assume it is pin connected on either end. The horizontal reaction would be 10 lbs. And the vertical reaction +10 lbs at one support and -10 lbs at the other.
 
Assume it is pin connected on either end. The horizontal reaction would be 10 lbs. And the vertical reaction +10 lbs at one support and -10 lbs at the other.

That's very slick and quick, but unfortunately not correct.

If you are going to get the right answers you need to do the job properly.
 
I guess you are questioning my supports? so pin connection on one end and roller on the other, Pin support vertical reaction is -10 lbs, horz reaction is -10 lbs, roller support is +10 lbs.
 
Sorry, should be -20 vertical at pin, -10 horz at pin and +20 vertical at roller.
 
Now that you understand why you cannot have two pinned joints - you then have three equations and four unknowns so you cannot solve them. Although in this case you can solve the vertical reactions only by using a moment condition as well as the vertical equilibrium.

Using the roller removes one of the unknowns so you can then solve for the other one.

Now to your second diagram.

In order to solve this you have to make some assumptions.

The assumption I would make would be that there is an even upward pressure.

This upward pressure may be replaced by a single force acting through the centroid of the line of pressure, equal in magnitude to the integral of pressure times area (or line length in this case).

Does this help?
 

Similar threads

Graduate Trying to understand couple stress in continua
  • · Replies 6 ·
Replies
6
Views
1K
Undergrad Newton's Third Law: Action & Reaction Along the Line Connecting Two Objects
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Distributed Forces and force density....
  • · Replies 8 ·
Replies
8
Views
3K
When are reactive forces enough to support this body?
  • · Replies 14 ·
Replies
14
Views
2K
High School Determine forces acting on double inclined plane
  • · Replies 13 ·
Replies
13
Views
2K
Undergrad What Is the Instantaneous Center of Rotation and How Is It Chosen?
  • · Replies 19 ·
Replies
19
Views
4K
High School Beam on an inclined plane
  • · Replies 4 ·
Replies
4
Views
958
Undergrad Cylinder supported by two rollers
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Pressurized containers: Stress distribution and large displacements
  • · Replies 69 ·
3
Replies
69
Views
5K
Undergrad Why does the main muscle use the most energy in body movements?
  • · Replies 24 ·
Replies
24
Views
2K