Consider a tripod consisting of a tetrahedral space truss with a ball-and-socket joint at C. If the height and lengths of the horizontal and vertical members are given, what force is acting on members BC and BA, considering that a tensile force is applied at D? A free-body diagram is drawn, including all the reaction forces at A, B and C. The moment equilibrium condition at joint C is applied. The distances are expressed in terms of position vectors in three dimensions. Simplifying further and using the force equilibrium conditions, the vector components along i yield FAy. Similarly, equating the k coefficients to zero, gives FBx. Finally, equating the j coefficients, give FAx. Now, a free-body diagram at joint B is considered to calculate the forces FBC and FBA. The forces FBD, FBC and FBA can be expressed using the position vectors. Applying the force equilibrium condition at joint B, and equating the coefficients of i, j and k unit vectors to zero, yields the forces along BC and BA.