A computer-implemented method for simulating an entity comprising rigid, semi-rigid, and/or flexible components of materials, the method being executed in a simulation system, the simulation system including one or more computers having one or more central processing units with one or more computer displays having one or more simulation views to a user, and one or more databases, wherein the one or more computers and the one or more databases being in communication with and accessible via one or more communication networks, the simulation system further including tracking devices connected to the one or more computers, and haptic devices allowing the user to interact with the one or more computers by receiving tactile feedback, wherein the haptic devices, the one or more computer displays and the tracking devices are physically connected and fixed at specific distances and orientations with respect to each other by use of a rigid harness; the method comprising: defining a force-transmission parameter value trans i for each of the rigid, semi-rigid and/or flexible components of the entity; calculating a rigid mass of the entity according to the equation: m r = ∑ i n m i tran s i, wherein m r is the rigid mass of the entity, m i is the mass of one of the components of the entity and trans i is the force-transmission parameter value of said one of the components of the entity; calculating an acceleration for each of the components of the entity due to rigid motion according to the equation: X ̈ i r = f i m i tran s i; calculating an acceleration for each of the components of the entity due to deformation according to the equation: X ̈ i f = f i m i 1 − tran s i, wherein f i is a force acting on each of the components of the entity; obtaining a plurality of any of masses, positions, velocities and accelerations for each of the rigid, semi-rigid and/or flexible components of the entity; calculating a plurality of forces and optionally torques acting on each of the components of the entity using any of the obtained positions, velocities and accelerations; calculating one or more of any of positions, velocities and accelerations for each of the components of the entity by using the calculated plurality of forces, optionally torques, and one or more defined force-transmission parameter values; and displaying a two-dimensional or a three dimensional simulated view of a representation of the entity or sub-portion thereof by using the calculated one or more positions and any of the calculated one or more velocities or accelerations of the entity; wherein the obtaining step further includes obtaining one or more of any of positions, velocities and accelerations of the one or more haptic devices that sense any of positional information, rotational information, hand motion and other motion from a user input, and return one or more push-back forces to the user allowing the feel of any of resistance, collision, penetration, separation, cutting, tearing, breakage and other motions of one or more materials of the simulated entity. defining a force-transmission parameter value trans i for each of the rigid, semi-rigid and/or flexible components of the entity; calculating a rigid mass of the entity according to the equation: m r = ∑ i n m i tran s i, wherein m r is the rigid mass of the entity, m i is the mass of one of the components of the entity and trans i is the force-transmission parameter value of said one of the components of the entity; calculating an acceleration for each of the components of the entity due to rigid motion according to the equation: X ̈ i r = f i m i tran s i; calculating an acceleration for each of the components of the entity due to deformation according to the equation: X ̈ i f = f i m i 1 − tran s i, wherein f i is a force acting on each of the components of the entity; obtaining a plurality of any of masses, positions, velocities and accelerations for each of the rigid, semi-rigid and/or flexible components of the entity; calculating a plurality of forces and optionally torques acting on each of the components of the entity using any of the obtained positions, velocities and accelerations; calculating one or more of any of positions, velocities and accelerations for each of the components of the entity by using the calculated plurality of forces, optionally torques, and one or more defined force-transmission parameter values; and displaying a two-dimensional or a three dimensional simulated view of a representation of the entity or sub-portion thereof by using the calculated one or more positions and any of the calculated one or more velocities or accelerations of the entity; wherein the obtaining step further includes obtaining one or more of any of positions, velocities and accelerations of the one or more haptic devices that sense any of positional information, rotational information, hand motion and other motion from a user input, and return one or more push-back forces to the user allowing the feel of any of resistance, collision, penetration, separation, cutting, tearing, breakage and other motions of one or more materials of the simulated entity.