Rigid body dynamics: falling stick

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Discussion Overview

The discussion revolves around the dynamics of a falling stick, specifically analyzing the conditions under which it will either stick or slip upon contacting a table. The focus is on applying principles of rigid body dynamics, including free body diagrams (FBD) and equations of motion, to solve a homework problem involving kinetic and static friction.

Discussion Character

  • Homework-related, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant presents a free body diagram (FBD) and derives an equation for angular acceleration, α, as α = -(3/2L)gsinθ, based on the torque due to gravity acting on the center of mass of the stick.
  • Another participant attempts to relate the angular acceleration to the translational acceleration of the rod, proposing an equation for the x-acceleration that includes terms for angular acceleration and frictional forces.
  • There is a request for confirmation or feedback on the derived equations, indicating uncertainty about the correctness of the approach.
  • A participant expresses frustration at the lack of responses, suggesting a possible need for clarification or further discussion on the problem.

Areas of Agreement / Disagreement

The discussion does not show clear agreement or consensus among participants, as there are ongoing questions and requests for validation of the proposed equations and methods.

Contextual Notes

Participants have not fully resolved the assumptions regarding the forces acting on the stick, particularly in the x-direction, and the conditions under which the stick will slip or stick are not clearly defined.

Feodalherren
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Homework Statement


A stick of length L and mass m is falling on a table with kinetic friction uK and static friction uS. Find the equation that determines whether the rod will stick or slip.

If m = 10kg and L = 100cm, uS = 0.8, uK = 0.7 and initial theta = 30 degrees find the initial accel for stick and slip.

Homework Equations


Irod = (1/3)mL^2
M= r x F

The Attempt at a Solution


I'm so stuck.

I made an FBD but as far as I can see, there are no forces in the X-direction, so what exactly makes the thing slip?
 
Last edited:
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From my FBD:

Iα = -mg(L/2)Sinθ

then α = -(3/2L)gsinθ

so far so good?
 
By which the translational x-acceleration of the rod must be (taking positive x to the left):

Ax= -αRSinθ - uK*N / m

correct?
 
Nobody?
 

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