sentences:  For contact between two spheres of radii formula_21 and formula_22, the area of contact is a circle of radius formula_23.The equations are the same as for a sphere in contact with a half plane except that the effective radius formula_1 is defined as 
  
  This is equivalent to contact between a sphere of radius formula_1 and a plane.If a rigid cylinder is pressed into an elastic half-space, it creates a pressure distribution described by
  
  where formula_1 is the radius of the cylinder and
  
  The relationship between the indentation depth and the normal force is given by
  
  In the case of indentation of an elastic half-space of Young's modulus formula_32 using a rigid conical indenter, the depth of the contact region formula_33 and contact radius formula_23 are related by
  
  with formula_36 defined as the angle between the plane and the side surface of the cone.