Friction coupling

Friction \Fric"tion\, n. [L. frictio, fr. fricare, frictum,to
   rub: cf. F. friction. See {Fray} to rub, arid cf.
   {Dentifrice}.]
   1. The act of rubbing the surface of one body against that of
      another; attrition; in hygiene, the act of rubbing the
      body with the hand, with flannel, or with a brush etc., to
      excite the skin to healthy action.
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   2. (Mech.) The resistance which a body meets with from the
      surface on which it moves. It may be resistance to sliding
      motion, or to rolling motion.
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   3. A clashing between two persons or parties in opinions or
      work; a disagreement tending to prevent or retard
      progress.
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   {Angle of friction} (Mech.), the angle which a plane onwhich
      a body is lying makes with a horizontal plane,when the
      hody is just ready to slide dewn the plane.

   Note: This angle varies for different bodies, and for planes
         of different materials.

   {Anti-friction wheels} (Mach.), wheels turning freely on
      small pivots, and sustaining, at the angle formed by their
      circumferences, the pivot or journal of a revolving shaft,
      to relieve it of friction; -- called also {friction
      wheels}.

   {Friction balls}, or

   {Friction rollers}, balls or rollers placed so as to receive
      the pressure or weight of bodies in motion, and relieve
      friction, as in the hub of a bicycle wheel.

   {Friction brake} (Mach.), a form of dynamometer for measuring
      the power a motor exerts. A clamp around the revolving
      shaft or fly wheel of the motor resists the motion by its
      friction, the work thus absorbed being ascertained by
      observing the force required to keep the clamp from
      revolving with the shaft; a Prony brake.

   {Friction chocks}, brakes attached to the common standing
      garrison carriages of guns, so as to raise the trucks or
      wheels off the platform when the gun begins to recoil, and
      prevent its running back. --Earrow.

   {Friction clutch}, {Friction coupling}, an engaging and
      disengaging gear for revolving shafts, pulleys, etc.,
      acting by friction; esp.:
      (a) A device in which a piece on one shaft or pulley is so
          forcibly pressed against a piece on another shaft that
          the two will revolve together; as, in the
          illustration, the cone a on one shaft, when thrust
          forcibly into the corresponding hollow cone b on the
          other shaft, compels the shafts to rotate together, by
          the hold the friction of the conical surfaces gives.
      (b) A toothed clutch, one member of which, instead of
          being made fast on its shaft, is held by friction and
          can turn, by slipping, under excessive strain or in
          starting.

   {Friction drop hammer}, one in which the hammer is raised for
      striking by the friction of revolving rollers which nip
      the hammer rod.

   {Friction gear}. See {Frictional gearing}, under
      {Frictional}.

   {Friction machine}, an electrical machine, generating
      electricity by friction.

   {Friction meter}, an instrument for measuring friction, as in
      testing lubricants.

   {Friction powder}, {Friction composition}, a composition of
      chlorate of potassium, antimony, sulphide, etc, which
      readily ignites by friction.

   {Friction primer}, {Friction tube}, a tube used for firing
      cannon by means of the friction of a roughened wire in the
      friction powder or composition with which the tube is
      filled.

   {Friction wheel} (Mach.), one of the wheels in frictional
      gearing. See under {Frictional}.
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