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How is this system in equilibrium?

  • Thread starter Peppino
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  • #1
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[diagram attached]

Assume some friction between M and the surface.

The forces acting on the connector point are the forces of friction of the M blocks and the weight of m, but they are in different directions; how do they manage to cancel out?
 

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  • #2
CWatters
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By being in opposite directions.

Aside: If the string (?) joining the blocks really was horizontal the tension would be infinite so it must sag a bit. Assume it sags to an angle θ with the horizontal. Then look at the horizontal and vertical components. The vertical components adds to the normal force on the blocks. The horizontal force is opposed by friction etc.
 
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  • #3
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But the weight of m is perpendicular to the frictional forces
 
  • #4
CWatters
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But the weight of m is perpendicular to the frictional forces
There are other vertical forces.

See my earlier reply that I edited.
 
  • #5
CWatters
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Can I check the line joining the blocks is indeed something like string and not a rigid rod?
 
  • #6
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Yes. Sorry I thought that was implied.

Ah, I see now. It is physically impossible for the strings to be 100% perpendicular, correct?
 
  • #7
CWatters
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Yes because the Tension in the string is T = mg/sin(θ) and sin(θ) approaches zero. Perhaps draw it with the string forming a V and work out all the forces.
 

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