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The use of momentum currents to improve qualitative reasoning models in the domain of mechanical oscillators Public Deposited

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  • Qualitative reasoning programs use a modelling language to discover the function of a mechanical device and a theory of causality to explain the reason for the device's behavior. A library of reusable model pieces for linear mechanical oscillators was developed for use with a causality theory developed by Forbus called Qualitative Process Theory. Difficulties in extending the library to include the case of sliding friction motivate a reformulation of the model from sum of forces to rate of momentum flow. It is shown how to decide if a quantity is "substance-like" or conserved or both. Substance-like quantities produce currents which can carry energy. Examples of substance-like quantities are momentum, mass, entropy, and electric charge. Momentum can be made to flow if an object is deformed or if two objects in contact are in relative motion. The new ontology allows graceful extension to sliding oscillators with friction and to hanging weights and coupled oscillators.
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