2.080 Structural Mechanics Energy Methods in Elasticity
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چکیده
We seldom measure H from the center of earth. Therefore what we can easily measure is the change of the potential energy ∆W = (mg)(H −Ho) (8.2) The energy is always positive. It can e zero but it cannot be negative. The gravity force F = mg is directed towards the center of earth. Therefore there is a need for the negative sign in Eq. (8.2)). In the coordinate system of Fig. (8.1), the gravity force is negative (opposite to the sense of coordinate x). The force F is acting in the sense of x but the difference H −Ho is negative. Extending the concept of the potential energy to the beam, the force is F = q dx and the w = H −Ho is the beam deflection. W ≡ + ∫ l
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