{
 "title": "Coulomb friction: a block pressed on another and slid (implicit mortar contact)",
 "kind": "theory",
 "source": "Coulomb's law of dry friction: a sliding interface carries μ_k times the normal force against the slip (C. A. Coulomb, Théorie des machines simples, Mém. Math. Phys. Acad. Sci. 10:161–332, 1785; P. Wriggers, Computational Contact Mechanics, 2nd ed., Springer 2006, §5.2)",
 "quantities": [
  {
   "id": "kinetic",
   "quantity": "the tangential over the normal force across the sliding interface",
   "measure": {
    "from": "slide",
    "pointer": "/contacts/0/force/0",
    "over": {
     "from": "slide",
     "pointer": "/contacts/0/force/2",
     "scale": -1.0
    }
   },
   "value": 0.2,
   "tolerance": {
    "relative": 0.001
   },
   "reason": "once the interface slips its friction is μ_k N exactly (the return map puts every slipping node's traction on the cone); the force opposes the upper block's motion"
  },
  {
   "id": "balance",
   "quantity": "the tangential contact force on the upper block over the sideways reaction at its top (they balance)",
   "measure": {
    "from": "slide",
    "pointer": "/contacts/0/force/0",
    "over": {
     "command": "results.reactions",
     "params": {
      "step": "Slide",
      "sets": [
       "top"
      ]
     },
     "pointer": "/sets/0/force/0"
    }
   },
   "value": -1.0,
   "tolerance": {
    "relative": 1e-06
   },
   "reason": "the friction carries the whole sideways load"
  },
  {
   "id": "slipping",
   "quantity": "the secondary nodes that slip (all 9)",
   "measure": {
    "from": "slide",
    "pointer": "/contacts/0/slipping_nodes"
   },
   "value": 9.0,
   "tolerance": {
    "exact": true
   },
   "reason": "a sideways demand far beyond μ N slips the whole interface"
  }
 ]
}