Upcoming Classes Tuesday, Oct. 9th Dissecting the iPod Assignment due: * Homework #4 (Egg container) Thursday, Oct. 11th Design at the Nexus Assignment due: * Topic and outline for second paper or oral presentation
Upcoming Deadlines Thursday, October 11th Outline of second oral presentation or written paper Tuesday, November 6th Second Set of Oral Presentations Second term paper (if not presenting)
Oral Presentations (II) The following persons will give oral presentations on Tuesday, November 6th : • Luttrell,Katherine • Macdonald,Keith • McDonald,Kathleen • Mendoza,Jazmin • Nguyen,Jennifer • Nguyen,Linda For everyone else, term paper is due on that date.
Extra Credit: SF Museum of Art Visit San Francisco Museum of Modern Art and see Abstract Expressionist paintings. Turn in your ticket receipt ($7 for students). Worth one homework assignment; deadline is Oct. 16th Guardians of the Secret, Jackson Pollock, 1943
Extra Credit: San Jose Ballet See a performance of San Jose Ballet in San Jose Center for Performing Arts (Nov. 15th – 18th ). Turn in your ticket receipt. Worth one homework assignment or three quiz/participation credits. Ramon Moreno in CARMINA BURANA
Two Fundamental Forces There are two fundamental forces in the universe: • Gravitational force • Electrical force All other forces are actually a result of one of these two fundamental forces.
Non-fundamental Forces All familiar forces, such friction and pressure, are due to the two fundamental forces Chemical reactions, such as burning, also due by electrical forces between molecules Contact forces between materials are due to electrical forces between molecules Weather due to buoyant motion of air (gravity) and solar radiation (electromagnetic)
Newton and the Moon Newton realized that Earth’s gravity was the centripetal force that kept the moon in orbit. Also discovered that gravity was weaker at that great distance. Gravity force That a force could act at a distance was a revolutionary concept
Gravity & Distance We don’t notice that gravity gets weaker as we move away from Earth because we rarely go very far. Moon is 30 Earth diameters away
At twice the distance, the face is ¼ the size. At four times the distance face is 16th the size. Area & Distance These four figures are equally spaced in distance and, in perspective, you are standing that distance from the first.
1 2 3 4 Demo: Perspective Cards Hold large card at arm’s length. Close one eye then hold small card at a distance such that it is same size as large card. That distance will be half way between your eye and large card. 1 Arm’s length Half
Inverse Square Law 1/4 Earth Gravity Gravity force weakens with distance as the inverse of the square of the distance. Geometric property of area and distance. Earth Gravity Outer circle is twice Earth’s radius so it has 4 times the area
Universal Law of Gravity Force of gravity has magnitude given by (Gravity Force) = (G) x ( Mass of Object A ) x ( Mass of Object B) ( Distance ) x ( Distance ) DISTANCE Object A Object B Force Force Equal and opposite forces (Newton’s Third law)
Universal Gravity Constant, G In the formula for gravity force, we have G = 0.0000000000667 N m2 / kg2 = 6.67 x 10–11 N m2 / kg2 The formula and the constant are called “universal” because, up to now, this theory predicts gravity anywhere in the universe.
Cavendish Experiment For non-astronomical objects gravity force is very small. Need sensitive balance to detect. First measured by Cavendish in his home laboratory in 1797 at age 67.
Salvador Dalí Salvador Dalí, (1904-1989) was a flamboyant Catalan-Spanish painter who popularized Surrealism. Dalí had a life-long interest in science, which influenced many of his compositions.
Dalí & Special Relativity The Persistence of Memory (1931) Time is not absolute but instead is relative to motion by the universality of electromagnetic radiation (i.e., the speed of light), as shown by Einstein in his theory of special relativity published in 1905.
Dalí & Quantum Mechanics In his "Anti-Matter Manifesto“ (1958), Dalí wrote, In the Surrealist period I wanted to create the iconography of the interior world and the world of the marvelous, of my father (Sigmund) Freud. Today the exterior world and that of physics, has transcended the one of psychology. My father today is Dr. (Werner) Heisenberg. The Disintegration of the Persistence of Memory, 1952–1954 Werner Heisenberg (1901-1976) introduced the uncertainty principle of quantum mechanics, which states that there are fundamental limits on what can be known. Heisenberg won the Nobel prize in Physics at the age of 31.
Dalí & Gravity Gravity is distorted or absent in many of Dali’s paintings Dream Caused by the Flight of a Bumblebee around a Pomegranate a Second Before Awakening (1944)
Dalí & Gravity Dalí Atomicus, photo by Philippe Halsman in collaboration with Salvador Dalí, 1948
Making of Dalí Atomicus Dalí and Halsman were mesmerized by the idea of suspension captured in a photograph. They argued back and forth on aspects of the composition, such as blowing up a chicken and whether to use milk or water. In his New York studio, Halsman suspended an easel, two paintings by Dalí (one of which was “Leda Atomica”), and a stepping stool while having his wife, Yvonne, hold a chair in the air. On the count of three, his assistants threw three cats and a bucket of water into the air; and on the count of four, Dalí jumped and Halsman snapped the picture. While his assistants mopped the floor and consoled the cats, Halsman went to the darkroom, developed the film, and reemerged to do it again. “Six hours and twenty-eight throws later, the result satisfied my striving for perfection,” wrote Halsman in his book Halsman on the Creation of Photographic Ideas. “My assistants and I were wet, dirty, and near complete exhaustion—only the cats still looked like new.”
Freefall & Weightlessness Freefall is a state of weightlessness, even though gravity is present.
NASA’s “Vomit Comet” NASA has a special airplane for training astronauts in free-fall weightless conditions. The “Vomit Comet” nickname tells you it’s quite a wild roller-coaster ride. The plane flies between 20,000 and 30,000 feet, same as commercial flights.
Flight of the “Vomit Comet” Weightless Freefall At the top of the arc, the plane’s trajectory is projectile motion. Pull out of Dive Power Climb Boeing 707 (modified)
Einstein’s General Relativity General relativity, published by Einstein in 1915, unifies special relativity and Newton's law of universal gravitation. In this theory gravitation is due to the curvature of space-time produced by the mass-energy.
Einstein’s Argument Imagine a box on Earth and one in space
Equivalence Principle Motion of objects looks the same whether or not the acceleration is due to gravity. Push
Einstein’s Argument Because light travels with constant speed, in the accelerating box light is deflected. Push
Einstein’s Argument In the time that it takes the light beam to cross the length of the box, the box has moved upward some distance. Appears as if the light is deflected downward Distance the box travels upward Push
Light Deflected by Gravity By Equivalence Principle Even though it has no mass, light is deflected by gravity, which has been astronomically confirmed.
Electric Charges and Forces There are two types of charge: positive charges and negative charges REPEL REPEL ATTRACT Like charges repel, opposite charges attract.
Electrons, Protons, & Atoms Electrons carry negative charge. Protons carry positive charge. Electrons are loosely bound to atoms Protons are tightly locked within the nucleus. Objects are usually neutral but can easily acquire or lose electrons to become charged. Helium atom Electrons Protons
Charging by Friction/Contact Electrons move easily so an object can become charged by rubbing electrons off the object’s surface. • Brush your hair with a plastic comb. • Walk across a carpet with plastic-soled shoes. Electrons taken off of fur onto rubber rod
Demo: Dial Electroscope Alternative design for electroscope Neutral Charged
Demo: Van de Graff Generator Van de Graff deposits large quantities of excess charge on its globe. A person with long hair can become a human electroscope.
Conductors & Insulators Materials, such as metals, in which electrons flow freely are called electrical conductors. Materials, such as plastic and wood, in which electrons do not move easily are called electrical insulators. Materials, such as silicon, that can act as conductors or insulators under different conditions are called semiconductors.
Plastic Insulators Plastic insulation on step of van de Graff and charge wand keep charge from leaving the metal balls. Plastic insulation on wire prevents charge to leave wire except at the ends, where the conducting metal is exposed.
Demo: Tesla Coil Air is an insulator but at high voltages it can conduct electricity as lightning. Portable Tesla coil
Tesla Coils Very high voltages achieved by large Tesla coils. Homemade, backyard model Fry’s Superstore, Fremont CA
Coulomb’s Law Electric force has magnitude given by (Electric Force) = (k) x ( Charge of Object A ) x ( Charge of Object B) ( Distance ) x ( Distance ) DISTANCE Object A Object B Force Force Equal and opposite forces (Newton’s Third law)
Demo: Induce the Can Charges separate in the can. Force of attraction is stronger since opposite charges are closer. Charged Object Can Rolls Metal Can (Neutral) + + + + Repulsion Force Attraction Force + +
Negatively charged rod repels electrons so they move as far away as possible. + + + + + + Demo: Electroscope & Induction The legs of the electroscope separate when charged rod brought near the electroscope. Charge induction pushes electrons into the legs. “Legs”
Lightning Storms Charge separates inside of thunderclouds. The lower part of the cloud is negatively charged. This induces a positive charge on the ground. When the voltage difference is high enough, a lightning bolt can occur.
Charge Polarization Charge polarization occurs when the positions of the electrons and protons in an atom are skewed. Polarized Atoms Polarized Neutral Charged Rod
Demo: Static “Cling” Charged object attracts a neutral insulator by inducing charge polarization in the neutral object. Charged Balloon Polarization Polarization Charged Comb Neutral Paper Neutral Wall
Next lecture we’ll see how everything in this store works Electric Current More important than static electricity is electric current, when charges move.
The Third Force Gravitational and electrical force are the two forces we regularly experience but there’s actually third universal force in nature: the nuclear force Explosion of an atomic bomb The Sun, photographed from space
Next LectureDissecting the iPod Remember: Assignment due: Homework #4 Egg package design & prototype