What's the meaning of <friction> tag under Joint->axis->dynamic

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Hi, there,

In the documentation, the definition of <friction> is "The physical static friction value of the joint.", then is it a force, torque or just a friction coefficient?

One link of my model will bend under the gravity from initial position around its joint axis, I just want to prevent this happening, so I tried to set the value between <friction> tag, but no matter what value I set it, the bending will still happen and won't even slow down. So anyone know any way to stop it? Or know the mechanism how this "friction" works?

Thanks!

The code for that joint is:

   <joint type="revolute" name="Center_hinge">
      <pose>0 0 0 0 0 0</pose>
      <child>UHolderBody</child>
      <parent>CircuitHolder</parent>
      <axis>
        <dynamics>
          <!--amping>0.20000</damping-->
          <friction>1000</friction>
        </dynamics>
        <xyz>1 0 0</xyz>
        <limit>
          <lower>-1.5707963</lower>
          <upper>1.5707963</upper>
        </limit>
      </axis>
    </joint>