CHAPTER 2 



Some Physical Forces Exemplified 



in Man 



(Mechanical; Osmotic; Electrical) 



All physical reality is a manifestation of what force does. On the ques- 

 tion of what force is, science can do no better than to call it by other names. 

 (Truth is a virtue, however inconvenient.) 



INTRODUCTION 



Force and energy, along with optics and acoustics, are the concerns of 

 classical medical physics, and some of the principles have been understood 

 for well over a hundred years. In this chapter the nature and the units of 

 force are reviewed, and the relationship between force and energy discussed. 

 The transfer of energy is reserved for Chapter 7. 



The living system is in a state of continual exchange of force and energy 

 with the environment. What is force? According to Newton (1687), it is vis 

 impressa, an influence, measurable in both intensity and direction, operating 

 on a body in such a manner as to produce an alteration of its state of rest or 

 motion. Generically, force is the cause of a physical phenomenon. It is 

 measured by its effect. Further penetration of the nature of force seems 

 destined to remain a philosophical question, because the range of experi- 

 ment stops at measurement of the effects. 



By experiment it is possible to measure the effect of different forces on the 

 same object, and devise a system of interconversion factors by which one 

 kind of force is related to another (for example, mechanical to osmotic). Ef- 



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