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M11 Revised Lecture Friday, March 01, 2013 5:47 PM Slides Notes Title Four Forces: Gravitational Force (this module) Electromagnetic Force (next module) Strong Force and Weak Force (module 13) ----------------------- Gravitational Force This one is the easiest to experience of the four forces. Sir Isaac Newton was the first scientist to realize that the gravity that makes something drop is the same as what causes planets to orbit the sun. ----------------------- Universal Law of Gravity The equation that he came up with for the Universal Law of Gravity is beyond your abilities at this point, but you can learn his 3 general principles: 1. All objects with mass are attracted to each other 2. The force of attraction is directionally proportional to their mass. 3. The force is inversely proportional to the square of the distance between the objects ----------------------- Then there is a Math Pag e ... Force and Circular Motion Centiptdal Force: Force that is always directed perpendicular to the velocity of the object. Centripetal acceleration: Circle at a constant speed, but because the direction keeps changing it actually works out to be acceleration. 1. Circular motion requires centripetal force 2. The larger that force, the faster the object travels in a circle 3. The larger centripetal force, the smaller the circle of motion. ---------------- Lab 11.1 Solar System Eliptical orbit plus axis tilt equals season. INNER: Mercury is at 1/90 Venus is at 2/90 (warmest, surprise! - thick atmosphere lots of CO2) Earth is at 3/90 Mars is at 5/90 OUTER. Massive Gas Planets Jupiter, just beyond 15/90 (rings) Saturn would be at 30/90 (rings) Uranus just before the 60/90 (rings) Neptune near 90/90 Objects orbit planet = satellite (moon) Perturbations - variations in the orbit often caused by other planets that are also orbiting. Neptune was found because of the perturbation of the orbit of Uranus Asteroids and Meteors: Pictured is the meteor that was such a surprise in Russia. There was an asteroid in February 2013 that was closer than many satellites but it was not expected that anything would hit the planet. Surprise. Just before the main asteroid came through the same day Russia was hit with this one. When is it an asteroid and when a meteor? What is a meteorite? ----------------------- Comets and Meteors Coming Soon - Comets Comet C/2011 L4 (PANSTARRS) in March ISON is a sungrazer that will been seen October through January 2013 C2013 A! may impact Mars October 2014 and we will be in the debris field from impact on 1st of October 2015 Gravity works on comets as well. Comets have the nickname of dirty snowballs since they are mostly ice, dirt, and dust. The ice isn't just frozen water though, it is frozen carbon dioxide, ammonia, and methane. Comets are typically less than 150 miles in diameter and orbit our sun as the planets do but in a very elliptical orbit. They get a brilliant tail when they are close to the sun because the sun's heat sublimes the frozen material instantly to a gas skipping the liquid phase because there is so much heat. This emits light. The brightest part is the nucleus of the comet which is the head. The fuzzy looking halo around the comet is called the coma. The tail always points away from the sun because it is formed not from velocity but from the solar wind that pushes out from the sun. The heat from the sun caused the comet to disintegrate more and more with each pass until they disappear altogether. Short period comets take 3 to 9 years to make an orbit and they seldom go any further away from the sun than Jupiter. These come from the Kuiper Belt which the Huble telescope confirmed existed in 1992. Collisions in this belt will cause material to start falling toward the sun becoming a comet. Long orbit comets go further out than the planets. Haley's Comet and Hale-Bopp are of this type. The last category is the very long-period comets. They go to the outer edges of the solar system and take 5,000 or more years to make their orbits. The theory is that these come from the Oort cloud. The Oort cloud was proposed in 1950 by a Dutch scientist. I bet you can guess what his last name was. Yes, Oort. --------------------------- What Causes Gravitational Force? In 1916 Albert Einstein proposed his General theory of Relativity. One of the byproducts was explaining what causes gravity. He explains that space actually bends in the presence of an object. His math equations explained Mercury's orbit perfectly. He also predicted that light too bends. Scientists were able to prove that light does indeed bend when it passes a star. Here is an experiment to help you understand the bending and how it influences motion in space. Lab 11.3 There is a competing theory, however. In this theory, objects exchange something called gravitons. They have to do this in a short period of time, so only when they are close or large can they do it in time. While we have no proof of this theory working on a large scale, it does seem to explain the weak force. We will be talking about this in an upcoming lesson. It is even possible that both theories are true and they work together. The bending of space causes the gravitons to get close enough to be exchanged, for instance. History of the View of Our Solar System Geocentric - Greek, 2nd century: Ptolemy, Heliocentric - Renaissance, 16th century: Copernicus 1543 (4 major moons of Jupiter and rings of Saturn, too) Galileo 1609 Brahe and Kepler at work on it at the same time - Kepler's Laws Newton -