Classical Physics
Overview of Classical Physics
Classical physics was basically a British enterprise. It started with Isaac Newton at Cambridge in the 17th century with his invention of the infinitesimal calculus and his formulation of the idea of a vector force as mass multiplied by acceleration. A vector is an arrow-like object with both a “magnitude” and a direction. When you add two vectors they form the sides of a parallelogram. The sum is the main diagonal. Newton also formulated the inverse square law of attractive gravitation explaining the motion of the planets and the trajectories of cannon balls in one formula. Since the same appears on both sides of Newton’s gravity equation, it cancels out, thereby explaining Galileo’s observation that all objects fall with the same acceleration (neglecting air resistance). The next great unification of the seemingly different pheneomena of electricity, magnetism and light was made by Scottish physcist, James Clerk Maxwell during the American Civil War. Maxwell’s equations consist of: Gauss’s law that says that the flux of electric force field lines surrounding a charge is proportional to that charge; the extended Ampere’s law that the circulation of magnetic field around a loop surrounding an electric current is proportional that current plus the rate at which any electric flux through the loop is changing (i.e., displacement current); Faraday’s induction law that the electric circulation around a loop is proportional to the rate at which any magnetic flux through the loop is changing; and the law of absence of magnetic monopoles which says that the total magnetic flux through any closed surface vanishes. That is, an equal number of magnetic lines enter as leave. Note, in the case of electric flux, the electric lines leave a positive charge and they enter a negative charge. All of these laws combined together yield a wave equation in vacuum in which light was shown to be transverse waves of vibrating electric and magnetic force fields at right angles to each other and to their direction of propagation. The most amazing fact was that the measured speed of high frequency light in vacuum was found to be equal to the inverse square root of the product of the electric permitivity and magnetic permeability of vacuum. Independent static measurements of these two quantities had been made in the nineteenth century along with pretty accurate measurements of the speed of light. The agreement was truly beautiful and elegant. Like Newton’s discoveries, Maxwell’s was a triumph of human intelligence. The English Industrial Revolution based on the steam engine stimulated the formulation of the laws of thermodynamics including the conversion of energy into different forms and the increase of disorder or entropy in thermally insulating systems. The entropy law placed strict limits on the possible efficiency of any kind of heat engine including the internal combustion engine. The entropy law also explains to some extent our perception of the flow of time from past to future.
A Classical Physics Course
