Laws of Mechanics of Engineering Mechanics
Newton’s Laws of Motion First law Every body remains in its state of either rest or of uniform motion unless its state is changed by external forces impressed upon it. SF = 0, SM = 0. Second law The rate of change of momentum is proportional to the impressed force and takes place in the direction of that force. The momentum may be linear or angular. Third law To every action there is always an equal and opposite reaction. Laws of Thermodynamics First law The change in total energy DE of a system is equal to the amount of heat dQ added to the system to the system minus the work dW done by the system. DE = dQ – dW Second law The change of entropy equals or exceeds the heat exchange divided by absolute temperature. Equations of Motion In a fluid flow the following type of forces may be present. 1. Gravity force, Fg . 2. Pressure force, Fp . 3. Force due to viscocity, Fu . 4. Force due to turbulence, Ft . 5. Force due to compressibility, Fc . • Thus, from Newton’s second law max = (Fg ) x ...