Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
ASTR 1020 General Astronomy: Stars and Galaxies Section 010 G1B20 TR 11:00-12:15 Instructor: Webster Cash TA: David Schenck http://casa.colorado.edu/~wcash/APS1020/APS1020.html Announcements .. .. Website http://casa.colorado.edu/~wcash/APS1020/APS1020.html First Homework Due January tbd First Observatory January 31 at 7pm Swirling Gas Falls into “Disk Stability” 99.9% Ended in Sun (0.1% in Jupiter) Probably the Same Around All Stars -- Planets are Common Shoots Planet-Size Bullets into Space Some Physics • Scientific Method • Hypothesis and Experiment • THERE IS A TRUTH!!! “I Think Therefore I Am” • If Experiment Shows Theory Wrong Then Its Wrong • Doesn’t Mean Theory is Right Galileo • • • • • First Great Modern Scientist Quantitative Analysis Tenacious Pursuit of Truth Challenged Aristotle and Church Used Telescopes to Demolish Old Solar System View • Persecuted In Italy – Celebrated Elsewhere Isaac Newton (1643-1727) • Greatest Scientist of All Time • Quantitative Prediction • Mechanics, Optics, Math – Theory & Observation Two Basic Concepts Mass – Amount of Matter (Not Weight) Inertia – Tendency of Objects to Have Unchanged Motion Newton’s Laws • Law #1: A body at rest or in motion remains that way unless acted upon by an outside force. • Law #2: a=F/m • Law #3: For every action there is an equal and opposite reaction. Law #1 A body in motion remains that way unless acted upon by an outside force. No Forces Contact Forces (electrical) Gravity Question A hockey rink is a frictionless surface. If a hockey player falls down, how is it that he is not moving in a straight line at constant velocity? a) The Earth’s gravity is acting as an outside force. b) Electrical forces in the rink force him off the straight line c) He must push off against another player d) He IS moving along a straight line. Law #2 F=ma a=F/m F = Force m = mass a = acceleration • Have a mass • Apply a force • Acceleration Results Note: Law #1 is special case of Law #2 (F=0 a=0) Question If there is no force on an object how is that the object can keep moving? a) Velocity is conserved in the Universe b) Momentum cannot be changed c) Velocity is independent of accleration d) The object needs energy to keep moving Motion Position X1 marks position in space at time t1 X2 marks position in space at time t2 Velocity Acceleration x2 x1 v t 2 t1 Change of Position with time v1 is velocity at time t1 v2 is velocity at time t2 v2 v1 a t 2 t1 Change of Velocity with time Example of Law #2 Push Your Car ---- Large m implies large F to get any a Let m = 1000kg If you apply 20N (Newtons is the unit of force) a=20/1000=.02m/s2 ---- accelerates .02m/s for every second you push Push for 10 seconds --- car will be moving .02m/sx10s= 0.2m/s (if on ice so no friction) (friction is yet another force) Law #3 For every action there is an equal and opposite reaction. For every ma there is an equal and opposite ma. Big one doesn’t move much Equal Mass Implies Equal Acceleration But What is F? a=F/m not enough because we don’t know what F is. Need a new law to describe forces There are Four KNOWN Forces Gravity Weak Nuclear Force Electromagnetism Strong Nuclear Force In order of strength Gravity Weakest Newton’s Law of Universal Gravitation Gm1m2 F21 r2 Gm1m2 F12 r2 (Law #3 Satisfied) G = 6.7x10-8 dyne.cm2/g2 in cgs units Value of G is measured. Nobody knows why it is the value it is. Electrical Force Equation Similar e1e2 Fe 2 r But What is a Force? Newtons Laws Give Value, and Show what to do. Force is an Exchange of Virtual Particles