Work and Energy:
When a body initially in equilibrium with its surroundings is subjected to external body and surface forces it deforms and eventually reaches a new equilibrium.
Here we want to estimate the work done by the external agency to bring about the change in the configuration of the body. From first law of thermodynamics the energy budget can be written as:
Incremental work done on the body (dW) + incremental heat supplied to it (dQ)= increase in its kinetic energy (ΔKE)+ increase in its intrinsic energy
=> dW + dQ = ΔK.E. + dU |
(3.1) |
K.E.
For small displacements the kinetic energy per unit volume can be expressed by  , where ρ is the density in the unstrained state. The rate at which the kinetic energy increases can be expressed as,
in which we can substitute the expressions from equation 2.12 to obtain,
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