In the above [Lagrange-Euler] equations, there are three types of terms. The first involves the second derivative of the generalized co-ordinates. The second is quadratic in q ˙ ˙ where the coefficients may depend on q . These are further classified into two types. Terms involving a product of the type q ˙ ˙ i 2 are called centrifugal forces while those involving a product of the type q ˙ ˙ i q ˙ ˙ j for i ≠ j are called Coriolis forces. The third type is functions of q only and are called gravitational forces.