Determining the direction of friction

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Homework Help Overview

The discussion revolves around determining the direction of friction for member AB in a system involving multiple members and forces, specifically focusing on the interaction between members AB and BC under the influence of an external force P.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the relationship between the impending motion of member BC and the resulting friction at point B for member AB. Questions arise regarding the direction of friction and the conditions under which it acts.

Discussion Status

The discussion includes attempts to clarify the reasoning behind the direction of friction for both members. Some participants suggest that the friction on member AB must counteract the motion of member BC, while others question the assumptions made about the direction of forces involved.

Contextual Notes

There is an emphasis on understanding the net forces acting on the members and the conditions under which they remain stationary or in motion. The discussion reflects uncertainty about the implications of the forces and the friction directions based on the provided diagrams.

OmniNewton
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Homework Statement


Given the following diagram:
media%2Ffba%2Ffba8deae-1663-4007-894c-9fa8d182da84%2FphpfPHlTg.png

When examining the FBD for member AB how does one determine the direction of friction at B? If surfaces B and C exhibit friction.

Homework Equations


N/A

The Attempt at a Solution


I know that impending motion for post BC is in the direction of P so friction acts opposite but I am unsure as to how one determines the impending motion for Member AB.
The answer provided is that the friction for member AB at surface B acts horizontally in the same direction as P.
 
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OmniNewton said:

Homework Statement


Given the following diagram:
media%2Ffba%2Ffba8deae-1663-4007-894c-9fa8d182da84%2FphpfPHlTg.png

When examining the FBD for member AB how does one determine the direction of friction at B? If surfaces B and C exhibit friction.

Homework Equations


N/A

The Attempt at a Solution


I know that impending motion for post BC is in the direction of P so friction acts opposite but I am unsure as to how one determines the impending motion for Member AB.
The answer provided is that the friction for member AB at surface B acts horizontally in the same direction as P.
The motion of member BC produced by the force P will create a friction force at B which opposes the motion of BC. That's the force which is shown on the FBD for member AB at point B.
 
SteamKing said:
The motion of member BC produced by the force P will create a friction force at B which opposes the motion of BC. That's the force which is shown on the FBD for member AB at point B.
Would the force at of friction on member BC not be in this direction <----- so why is Member AB's force of friction in this direction ------> ?
 
OmniNewton said:
Would the force at of friction on member BC not be in this direction <----- so why is Member AB's force of friction in this direction ------> ?
As long as member AB is not moving, the net force between AB and BC must equal zero. When you draw a FBD of AB, a force opposite the friction force on BC must be included to bring the net force on this member to zero.
 
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Alright thank you sir!
 

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