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3 Mechanical Aspects of Biosystems
3.1 Newtonian Principles in Biostatics and Biodynamics
Never trust an experimental result until it has been confirmed by theory.
—Sir Arthur Stanley Eddington
Newtonian principles enter biology from the scale of macromolecules to that of
the largest animals. Life systems intrinsically involve forces. On the microscopic
level, nuclear and electric forces allow atomic structures, and therefore chemistry.
Weak interactions have practically an unmeasurable force outside the nucleus of
atoms, but are the cause for radioactive decay, a factor in genetic mutation. With
the known forces and particles, biochemistry and the evolution of life become
understandable as a natural process at the atomic and molecular level. On a
nanometer scale, the activity around biostructures can be formulated in terms of
predominantly electrical forces. For more massive biosystems evolving on a planet,
organisms must also cope with gravitational forces. The dominance of electrical
and gravitational forces in the interactions within biological systems comes from
the long-range behavior of these forces, which is in contrast to nuclear and weak
forces, which are short range. These latter two drop exponentially outside a range
the size of the nuclei of atoms. 1
Currently, to accurately predict the behavior of atomic and molecular systems,
quantum mechanics is applied, a topic we will reserve until our study of molecular
biophysics. As yet, no known life systems have traveled close to the speed of
light relative to us, so that for understanding biosystems, we can postpone explicit
consideration of Einsteinian mechanics. For the dynamics of life systems above the
molecular scale, Newtonian physics and a little statistics will be sufficient.
3.2 Newton’s Laws Applied to a Biosystem
Few things are harder to put up with than the annoyance of a good example.
—Mark Twain
3.2.1 Basic Concepts
Before discussing the effects of forces in biosystems, we will review some
physically defined concepts.
1 The exponential drop in the force can be associated in quantum theory with the exchange of
particles with mass, making the force proportional to exp (−μc r/ ¯
h)/r 2 , where r is the distance
from the charge center, ¯
h is Planck’s constant over 2π , μ the mass of the quantum in the field
causing the force, and c is the speed of light. The quanta of the electromagnetic interaction,
called photons, appear to have no mass (μ < 10 −14 eV/c 2 ), so the exponential factor becomes
one, characteristic of long-range forces.
3 Mechanical Aspects of Biosystems
3.1 Newtonian Principles in Biostatics and Biodynamics
Never trust an experimental result until it has been confirmed by theory.
—Sir Arthur Stanley Eddington
Newtonian principles enter biology from the scale of macromolecules to that of
the largest animals. Life systems intrinsically involve forces. On the microscopic
level, nuclear and electric forces allow atomic structures, and therefore chemistry.
Weak interactions have practically an unmeasurable force outside the nucleus of
atoms, but are the cause for radioactive decay, a factor in genetic mutation. With
the known forces and particles, biochemistry and the evolution of life become
understandable as a natural process at the atomic and molecular level. On a
nanometer scale, the activity around biostructures can be formulated in terms of
predominantly electrical forces. For more massive biosystems evolving on a planet,
organisms must also cope with gravitational forces. The dominance of electrical
and gravitational forces in the interactions within biological systems comes from
the long-range behavior of these forces, which is in contrast to nuclear and weak
forces, which are short range. These latter two drop exponentially outside a range
the size of the nuclei of atoms. 1
Currently, to accurately predict the behavior of atomic and molecular systems,
quantum mechanics is applied, a topic we will reserve until our study of molecular
biophysics. As yet, no known life systems have traveled close to the speed of
light relative to us, so that for understanding biosystems, we can postpone explicit
consideration of Einsteinian mechanics. For the dynamics of life systems above the
molecular scale, Newtonian physics and a little statistics will be sufficient.
3.2 Newton’s Laws Applied to a Biosystem
Few things are harder to put up with than the annoyance of a good example.
—Mark Twain
3.2.1 Basic Concepts
Before discussing the effects of forces in biosystems, we will review some
physically defined concepts.
1 The exponential drop in the force can be associated in quantum theory with the exchange of
particles with mass, making the force proportional to exp (−μc r/ ¯
h)/r 2 , where r is the distance
from the charge center, ¯
h is Planck’s constant over 2π , μ the mass of the quantum in the field
causing the force, and c is the speed of light. The quanta of the electromagnetic interaction,
called photons, appear to have no mass (μ < 10 −14 eV/c 2 ), so the exponential factor becomes
one, characteristic of long-range forces.