Welcome to Physics 43! Classical Mechanics! Study of the motion of objects and mechanical systems that are large relative to atoms and move at speeds much slower than the speed of light. You can’t get to Modern Physics without doing Classical Physics! The fundamental laws and principles of Classical Physics are the basis Modern Physics. Some Physical Models of the Universe A Brief History of Physics Physics seeks a single theory of Everything….and it always has… Bubble Universes Superstrings Theory of Everything (TOE) History is IMPORTANT The historical development of science shows us the process of discovery and the way our brains work and POSSIBLY the inherent biases and limitations of the rational mind. By studying the historical development of science we learn about the mistakes that have been made so hopefully we do not repeat them...and maybe we discover old ideas that still have something to teach us about the way the universe works…or at least, how our brains work… Let no one unversed in geometry enter here. The Universe is made of pure mathematical ideas – the Platonic Solids. Plato believed that the stars, planets, Sun and Moon move round the Earth in crystalline spheres. Earth and the universe were seen as constructed out of five basic elements: earth, water, air, fire, and ether. The natural place of the motionless Earth was at the center of that universe. The stars in the heavens were made up of an indestructible substance called ether (aether) and were considered as eternal and unchanging. The laws of nature of the Earth were different from those of the Heavens. The Sun and the planets would revolve in small circles whose centers revolve in large circles about the Earth ("epicycles") which is at rest and at the center of the Universe. From our perspective, the sun and stars appear to orbit us! Ptolemy's geocentric system, adopted by the Roman Catholic Church, dominated western thought until the time of Copernicus, 14 centuries later….. 5th-15th Centuries Developed science & medicine based on observation and experiment, rather than on conjecture creating the basis of what would later be called The Scientific Method. European Enlightenment Renaissance 14th & 15th Century The Vitruvian Man 1490 Copernicus put the Sun at the center of the solar system with the Earth orbiting around the Sun, thus proposing a heliocentric cosmology. Like Aristotle and Ptolemy, Copernicus retained the conventional idea that the planets moved in perfectly circular orbits and continued to believe that the stars were fixed and unchanging. REVOLUTION! I hold that the Sun is located at the centre of the revolutions of the heavenly orbs and does not change place, and that the Earth rotates on itself and moves around it. Galileo Challenged The Dogma Of Natural Motion with Experiments Heliocentric Heretics Rome, Campo de'fiori: The monument to Giordano Bruno, burnt at the stake here. The Trial of Galileo June 22, 1633: Galileo was convicted and sentenced to life imprisonment by the Catholic Inquisition. In 1992, the church finally lifted its edict of Inquisition against Galileo, who went to his grave a devout Catholic, despite the church’s treatment of him. Based on observational data he derived three laws of planetary motion that put the sun at he center of the universe with elliptical orbits. Kepler’s 3 Laws of Planetary Motion 1: The orbit of each planet about the sun is an ellipse with the sun at one focus. 2. Each planet moves so that it sweeps out equal areas in equal times. 3. The square of the orbital period of any planet is proportional to the 2 cube of the semimajor axis of the T1 elliptical orbit. 3 constant r1 Planet Orbits are Elliptical "The next question was - what makes planets go around the sun? At the time of Kepler some people answered this problem by saying that there were angels behind them beating their wings and pushing the planets around an orbit. As you will see, the answer is not very far from the truth. The only difference is that the angels sit in a different direction and their wings push inward." -Richard Feynman Isaac Newton (1642 -1727) Using his Calculus, Newton derives Kepler’s three laws of planetary motion from his own three laws of motion and his Universal Law of Gravity. Newton is the man of the millennium. In Principia (1687 ) Newton •Invented Calculus •3 Laws of Motion •Universal Law of Gravity Newton’s Principia in 1687. Galilean Relativity Space and Time are ABSOLUTE! u= u‘+v Velocities add: Newton’s First Law (Law of Inertia) An object will remain at rest or in a constant state of motion unless acted upon by external net forces. Newton’s 2nd Law F ma F a net m The acceleration of object is directly related to the net forces acting on it and inversely proportional to its mass. Newton’s 3rd Law FFhand on wall wall on hand To every force there is an equal but opposite reaction force. Universal Law of Gravity 1687 Every particle in the Universe attracts every other particle with a force along a line joining them. The force is directly proportional to the product to their masses and inversely proportional to the square of the distance between them. M d m mM F ~ d 2 Conservation of Energy Energy can neither be created nor destroyed. It may change in form or be transferred from one system to another. The total amount of energy in the Universe is constant and can never change. EEif Except for VERY brief amounts of time according to the Heisenberg Uncertainty Principle. Robert Hooke (1635-1703) •Leading figure in Scientific Revolution •Contemporary and arch enemy of Newton •Hooke’s Law of elasticity •Worked in Physics, Biology, Meteorology, Paleontology •Devised compound microscope •Coined the term “cell” 1800’s: Atomic Emission of Light Each chemical element produces its own unique set of spectral lines when it burns Fraunhofer Lines: 1814 The English chemist William Hyde Wollaston was in 1802 the first person to note the appearance of a number of dark features in the solar spectrum. In 1814, Fraunhofer independently rediscovered the lines and began a systematic study and careful measurement of the wavelength of these features. In all, he mapped over 570 lines, and designated the principal features with the letters A through K, and weaker lines with other letters. Kirkoff’s Rules for Spectra: 1859 German physicist who developed the spectroscope and the science of emission spectroscopy with Bunsen. Bunsen Kirkoff * Rule 1 : A hot and opaque solid, liquid or highly compressed gas emits a continuous spectrum. * Rule 2 : A hot, transparent gas produces an emission spectrum with bright lines. * Rule 3 : If a continuous spectrum passes through a gas at a lower temperature, the transparent cooler gas generates dark absorption lines. Anders Jonas Ångström 1869 Ångström measured the wavelengths on the four visible lines of the hydrogen spectrum, obtained with a diffraction grating, whose dispersion is linear, and replaced Kirchhoff's arbitrary scale by the wavelengths, expressed in the metric system, using a small unit (10-10 m) with which his name was to be associated. Line color Wavelength red 6562.852 Å blue-green 4861.33 Å violet 4340.47 Å violet 4101.74 Å Balmer Series: 1885 Johann Balmer found an empirical equation that correctly predicted the four visible emission lines of hydrogen Johannes Robert Rydberg generalized it in 1888 for all transitions: 1 1 1 R Hα is red, λ = 656.3 nm H 22 H is green, λ = 486.1 nm λn2 β Hγ is blue, λ = 434.1 nm RH is the Rydberg constant H is violet, λ = 410.2 nm 7 -1 δ RH = 1.097 373 2 x 10 m n is an integer, n = 3, 4, 5,… The spectral lines correspond to different values of n Why a discrete spectrum? Why THIS spectrum? Why this shape? Why the drop? Sadi Carnot: Father of Thermo (1796 –1832) 1824: A heat engine operating in an ideal, reversible cycle (now called a Carnot cycle) between two reservoirs is the most efficient engine possible. This sets an upper limit on the efficiencies of all other engines. Kinetic Theory/Thermodynamics • Gas Particles are in constant RANDOM motion • Particles have different speeds • Pressure : momentum transferred by particles colliding • Average KE of each particle is ~ T •Heat flows from hot to cold: Entropy Young’s Double Slit: Light is a Wave 1803 λL y m( m 0,, 1 2 ) bright d λL 1 ydark m ( m 0,, 1 2 ) d 2 Oscillating Charges Produce Radio Waves: 1887 Heinrich Hertz “I do not think that the wireless waves I have discovered will have any practical application." Frequency of EM wave is the same as the frequency of oscillation. 1896: Zeeman Effect The Zeeman Effect is the splitting of spectral lines when a magnetic field is applied. Einstein visiting Pieter Zeeman in Amsterdam, with his friend Ehrenfest. photo Zeeman took of the effect named for him (around 1920) 1860: E&M was Solved! (Vector Form) James Clerk Maxwell 1860s Light is wave. The medium is the Ether. 1 c3.0 x 108 m / s 0 o Measure the Speed of the Ether Wind The Luminiferous Aether was imagined by physicists since Isaac Newton as the invisible "vapor" or "gas aether" filling the universe and hence as the carrier of heat and light. Michelson-Morely Experiment 1887 The speed of light is independent of the motion and is always c. The speed of the Ether wind is zero. OR…. Lorentz Contraction The apparatus shrinks by a factor : 1/ vc22 A Problem with Electrodynamics The force on a moving charge depends on the Frame.