Consider a rod fixed to a wall, which can be pulled by a chain by applying a force at one of its ends. The position of the rod is defined using a three-dimensional coordinate system. The angle theta between the force vector and the rod, and the projection of force along the rod needs to be determined. First, the position vectors for the two ends of the rod are defined. Then the position vector along the rod is determined. The next step determines the magnitude of the position vector rAB and the force vector. Now, the dot product of the position vector with the force vector is determined by multiplying the components of the two vectors. Angle theta is then estimated as the inverse cosine function of the ratio of the dot product and the product of magnitudes of the two vectors. The projection of the force along the rod can be determined as the product of the magnitude of force and the cosine of theta.