Galileo’s principle

The inadequacy of the mechanical model of light first became apparent when the electromagnetic equation of motion was seen to violate Galileo s principle of relative motion. As derived by Maxwell, electromagnetic motion is described by a wave equation ... 

In order to understand the confusion, it has to be remembered that all designers and engineers over the past 400 years have been educated in Galileo s principle that failure depends on the stress, i.e. the negative pressure, in the material. This stress criterion of failure states that rupture occurs when the stress reaches a critical value. In mathematical terms this is Equation (15.2) which gives ultimate force proportional to area. 

The mechanical principle of relativity, coupled with the suggestion of uniformity of time flow in all inertial reference systems, is referred to as Galileo s principle of relativity. 

Einstein has generalized Galileo s principle of relativity. According to Einstein s principle of relativity, it is impossible by either mechanical or by physical experiment (in particular, electrical, magnetic or optical) conducted in an inertial system, to distinguish if this system is at rest or in rectilinear uniform motion. This statement is the basis of the special relativistic theory (see Section 1.6). 

In order to preserve the principles mentioned above, it was necessary to proceed further than Galileo s transformations (1.3.1) and (1.3.2). These transformations have been replaced by the mathematical Lorentz equations already known in physics. 

For physical objects and reference frames moving with speeds ixc or u< , Einstein s theory led to the results of classical nonrelativistic theory Lorentz transformations changed into Galileo s transforms and the Einstein relativity principle into Galileo s relativity principle. 

A short glance back into the past gives an interesting perspective on this question. Aristotle (350 BC) maintained that an iron ball falls faster than a feather, implying that the interaction of these two bodies with the Earth is different. Galileo (1604) has experimentally shown that all bodies fall with the same acceleration, a property known as the principle of universality of free fall. This principle can be derived from the Newton s gravitational law (1687) which, when combined with the Newton s equation of motion shows that the gravitational acceleration of all bodies is the same. 

Tlie general principle of conservation of energy was established about 1850. Tlie germ of tliis principle as it applies to mechanics was implicit in the work of Galileo (1564-1642) and Isaac Newton (1642-1726). Indeed, it follows directly from Newton s second law of motion once work is defined as tlie product of force and displacement. 

Boyle, Robert. (1627-1691). A native of Ireland, Boyle devoted his life to experiments in what was then called natural philosophy, i.e., physical science. He was influenced early by Galileo. His interest aroused by a pump that had just been invented, Boyle studied the properties of air, on which he wrote a treatise (1660). Soon thereafter, he stated the famous law that bears his name (see following entry). Boyle s group of scientific enthusiasts was known as the invisible college , and in 1663 it became the Royal Society of London. Boyle was one of the first to apply the principle that Francis Bacon had described as the new method —namely, inductive experimentation as opposed to the deductive method of Aristotle—and this became and has remained the cornerstone of scientific research. Boyle also investigated hydrostatics, desalination of seawater, crystals, electricity, etc. He approached but never quite stated the atomic theory of matter however, he did distinguish between compounds and mixtures and conceived the idea of particles becoming associated to form molecules. 

Galileo formulated some mechanical principles that enabled Newton to establish the physical basis of Kepler s laws. By noticing that a ball which rolls on a plane that slopes downward is accelerated and one on a plane that slopes upward is retarted, he argued that motion along horizontal planes should be uniform and perpetual. This view represents an important advance... 

Book iv of B is on chemical principles. In 1668 Duhamel met Boyle in England and two chapters in the second edition (1669) of B contain experiments on the elasticity of air and refer to Boyle s work on it. C refers to many modern authors, including Boyle, Bacon, Gilbert, Willis, Hooke, Gassendi, Descartes, Pascal, Galileo, Torricelli, Guericke, Tachenius, and Erasmus Bartholinus. Boyle quotes Du Hamel s praise in C of his own Experiments and Observations touching Coldy 1665. Duhamel was the first Secretary of the Academic Royale des Sciences (1666-97). 

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