Place of Heat Transfer in Engineering

Let us first review a well-known problem taken from mechanics. For this problem let us consider two formulations, based on different assumptions. Our concern will be with the nature of the physical laws employed m these formulations. (At this stage our discussion will be somewhat conventional the philosophy of the text will be set forth at the end of this chapter). 

Example Free fall of a body. Consider a body of mass m in a vacuum falling freely under the effect of the gravitational field g. We wish to determine the instantaneous location of this body. 

F being the sum of external forces and a the acceleration vector, gives in terms of vertical distance x 

In our second formulation of the problem, let us include the resistance to the motion of the body from the surroundings. With this consideration, we have 

As demonstrated by the foregoing two formulations, some problems taken from mechanics can be formulated by using only Newton s laws of motion these are called mechanically determined problems. The dynamics of rigid bodies in the absence of friction, statically determined problems of rigid bodies, and mechanics of ideal fluids provide examples of this class. Some other mechanics problems, however, require knowledge beyond Newton s laws of motion. These are called mechanically undetermined problems. The dynamics of rigid bodies with friction and the mechanics of deformable bodies provide examples of this class. 

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