Physics in Biology and Medicine (Complementary Science) 4th Edition

Book Preface

Until the mid 1800s it was not clear to what extent the laws of physics and chemistry, which were formulated from the observed behavior of inanimate matter, could be applied to living matter. It was certainly evident that on the large scale the laws were applicable. Animals are clearly subject to the same laws of motion as inanimate objects. The question of applicability arose on a more basic level. Living organisms are very complex. Even a virus, which is one of the simplest biological organisms, consists of millions of interacting atoms. A cell, which is the basic building block of tissue, contains on the average 1014 atoms. Living organisms exhibit properties not found in inanimate objects. They grow, reproduce, and decay. These phenomena are so different from the predictable properties of inanimate matter that many scientists in the early 19th century believed that different laws governed the structure and organization molecules in living matter. Even the physical origin of organic molecules was in question. These molecules tend to be larger and more complex than molecules obtained from inorganic sources. It was thought that the large molecules found in living matter could be produced only by living organisms through a “vital force” that could not be explained by the existing laws of physics. This concept was disproved in 1828 when Friedrich Wöhler synthesized an organic substance, urea, from inorganic chemicals. Soon thereafter many other organic molecules were synthesized without the intervention of biological organisms. Today most scientists believe that there is no special vital force residing in organic sub-stances. Living organisms are governed by the laws of physics on all levels.
Much of the biological research during the past hundred years has been directed toward understanding living systems in terms of basic physical laws. This effort has yielded some significant successes. The atomic structure of many complex biological molecules has now been determined, and the role of these molecules within living systems has been described. It is now possible to explain the functioning of cells and many of their interactions with each other. Yet the work is far from complete. Even when the structure of a complex molecule is known, it is not possible at present to predict its function from its atomic struc-ture. The mechanisms of cell nourishment, growth, reproduction, and commu-nication are still understood only qualitatively. Many of the basic questions in biology remain unanswered. However, biological research has so far not revealed any areas where physical laws do not apply. The amazing properties of life seem to be achieved by the enormously complex organization in living systems.

The aim of this book is to relate some of the concepts in physics to living systems. In general, the text follows topics found in basic college physics texts. The discussion is organized into the following areas: solid mechanics, fluid mechanics, thermodynamics, sound, electricity, optics, and atomic and nuclear physics.
Each chapter contains a brief review of the background physics, but most of the text is devoted to the applications of physics to biology and medicine. No previous knowledge of biology is assumed. The biological systems to be dis-cussed are described in as much detail as is necessary for the physical analysis. Whenever possible, the analysis is quantitative, requiring only basic algebra and trigonometry.
Many biological systems can be analyzed quantitatively. A few examples will illustrate the approach. Under the topic of mechanics we calculate the forces exerted by muscles. We examine the maximum impact a body can sus-tain without injury. We calculate the height to which a person can jump, and we discuss the effect of an animal’s size on the speed at which it can run. In our study of fluids we examine quantitatively the circulation of blood in the body. The theory of fluids allows us also to calculate the role of diffusion in the func-tioning of cells and the effect of surface tension on the growth of plants in soil. Using the principles of electricity, we analyze quantitatively the conduction of impulses along the nervous system. Each section contains problems that explore and expand some of the concepts.
There are, of course, severe limits on the quantitative application of physics to biological systems. These limitations are discussed.
Many of the advances in the life sciences have been greatly aided by the application of the techniques of physics and engineering to the study of living systems. Some of these techniques are examined in the appropriate sections of the book.
This new edition has been further updated and includes a discussion of atomic force microscopy, use of lasers in medical diagnostics and the applica-tions of nanotechnology in biology and medicine.
A word about units. Most physics and chemistry textbooks now use the MKS International System of units (SI). In practice, however, a variety of units continues to be in use. For example, in the SI system, pressure is expressed in units of pascal (N/m2). Both in common use and in the scientific literature one often finds pressure also expressed in units of dynes/cm2, Torr (mm Hg), psi, and atm. In this book I have used mostly SI units. However, other units have also been used when common usage so dictated. In those cases conversion fac-tors have been provided either within the text or in a compilation at the end of Appendix A.
In the first edition of this book I expressed my thanks to W. Chameides, M. D. Egger, L. K. Stark, and J. Taplitz for their help and encouragement. In the second edition I thanked Prof. R. K. Hobbie and David Cinabro for their careful reading of the manuscript and helpful suggestions. In this fourth edition I want to express my appreciation to Prof. Per Arne Rikvold for his careful reading of the text and his important comments. I also want to thank Patricia Osborn and Caroline Johnson editors at Elsevier/Academic Press for their great help in the preparation of this fourth edition of the book.

Paul Davidovits
Chestnut Hill, Massachusetts December 2012