In classical mechanics, holonomic constraints are relations between the position variables (and possibly time) that can be expressed in the following form: where are n generalized coordinates that describe the system (in unconstrained configuration space). For example, the motion of a particle constrained to lie on the surface of a sphere is subject to a holonomic constraint, but if the particle is able to fall off the sphere under the influence of gravity, the constraint becomes non-holonomic. For the first case, the holonomic constraint may be given by the equation where is the distance from the centre of a sphere of radius , whereas the second non-holonomic case may be given by Velocity-dependent constraints (also called semi-holonomic constraints) such as are not usually holonomic. Holonomic system In classical mechanics a system may be defined as holonomic if all constraints of the system are holonomic. For a constraint to be holonomic it must be expressible as a function: i.e. a holonomic constraint depends only on the coordinates and maybe time . It does not depend on the velocities or any higher-order derivative with respect to t. A constraint that cannot be expressed in the form shown above is a nonholonomic constraint. Introduction As described above, a holonomic system is (simply speaking) a system in which one can deduce the state of a system by knowing only the change of positions of the components of the system over time, but not needing to know the velocity or in what order the components moved relative to each other. In contrast, a nonholonomic system is often a system where the velocities of the components over time must be known to be able to determine the change of state of the system, or a system where a moving part is not able to be bound to a constraint surface, real or imaginary. Examples of holonomic systems are gantry cranes, pendulums, and robotic arms. Examples of nonholonomic systems are Segways, unicycles, and automobiles. Terminology The configuration space lists the displacement of the components of the system, one for each degree of freedom. A system that can be described using a configuration space is called scleronomic. The event space is identical to the configuration space except for the addition of a variable to represent the change in the system over time (if needed to describe the system). A system that must be described using an event space,