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Tensile and compressive forces

  1. Jan 9, 2016 #1

    MBBphys

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    Example of a tightrope walker:
    Figure_04_05_06.jpg
    Now, the weight force acts at a point. The rope is stretched. Compressive forces act inwards towards that point (opposite to TL and TR, the tensile forces). The resultant of the compressive forces equals the weight and is in the same direction – the weight force CAUSES the compressive forces.

    If the man is stable on the tightrope and not moving, then resultant force is zero.

    As string is stretched, tension forces act away from the point where weight acts (see image above). These are labelled TL and TR. The resultant of the tensile forces equals the weight in magnitude, but acts in the opposite direction, producing zero net force.

    Is my understanding correct? Thanks in advance for your reply :)
     
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  3. Jan 9, 2016 #2

    SteamKing

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    What compressive forces? The wire is placed in tension by the weight of the walker.

    You should know from experience that you can't push on a rope. Since you can't push on a rope, there is no compressive force.
    That is why it's called static equilibrium.
    The weight of the walker causes the line to deflect downward. The tensile force in each half of the rope can be resolved into a horizontal and a vertical component.

    For static equilibrium to occur, the sum of all these forces must equal zero.

    The two horizontal components are of equal magnitude acting in opposite directions, so their net force is zero.
    The sum of the vertical components of the tensile forces in the rope must equal the weight of the walker, and these components act in the opposite direction to the weight of the walker, so the net force in the vertical direction is zero.

    The sum of the forces in the horizontal and vertical directions is zero, therefore, the walker is in static equilibrium.
     
  4. Jan 10, 2016 #3

    MBBphys

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    Ah yes I get why I was wrong; thanks so much for your help :)
     
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