1PTYS_206_orbits_gravity - PYTS/ASTR 206 Orbits and Gravity...

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PYTS/ASTR 206 – Orbits and Gravity 1 Announcements D2L site up Homework 1 posted after class on website http://www.lpl.arizona.edu/~shane/PTYS_206 Look at the homework early! You have a week to finish – not a week to start! Due in class next Thursday TA is only Kevin Jones for now Priyanka will join us in ~3 weeks – please don’t visit her until then. Office hours: Kevin – Tuesday 2-4pm, Gould-Simpson 511 Myself – Tue./Thur. 1.45-4pm, Kuiper 524
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PYTS/ASTR 206 – Orbits and Gravity 2 Observations Craters, Trenches, Bright/white surface Higher ground on the right, more craters on the left
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PTYS/ASTR 206 – The Golden Age of Planetary Exploration Shane Byrne – shane@lpl.arizona.edu Orbits and Gravity
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PYTS/ASTR 206 – Orbits and Gravity 4 Gravity Newton and Galileo Planetary Shape Flattening The Geoid Tides Fate of the Moon Orbits of planetary objects Kepler’s laws In this lecture…
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PYTS/ASTR 206 – Orbits and Gravity 5 Gravity is one of 4 physical forces in nature Relatively unimportant on small scales …but it dominates the universe at large scales Where does gravity operate? Holds galaxies together Provides pressure for fusion reactions in stars Holds planets in their orbits Holds planets together
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PYTS/ASTR 206 – Orbits and Gravity 6 Objects that contain matter (they have mass) attract each other This attractive force is called gravity, e.g. Your body and the Earth The Moon and the Earth The Earth and the Sun Your body with a comet billions of km away The force of this attraction depends on three things Mass of the first object Mass of the second object What’s gravity?
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PYTS/ASTR 206 – Orbits and Gravity 7 Galileo was first to systematically investigate gravity Objects accelerate as they fall i.e. the longer the drop the faster they hit the ground All objects accelerate at the same rate The famous leaning tower of Pisa experiment Some doubt about whether this actually happened This acceleration is 9.8 m/s 2 0 m/s when you let it go 9.8 m/s after 1 seconds 2*9.8 m/s after 2 seconds etc… This acceleration is not the same on other planets e.g. it’s 3.7 m/s 2 on Mars
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PYTS/ASTR 206 – Orbits and Gravity 8 F = M 1 * a 1 F gravity = M 1 * a gravity What gives? Is gravity a force or an acceleration? It’s a force that produces an acceleration Isaac Newton developed modern mechanics – using three basic laws With no forces operating an object doesn’t change its momentum (m 1 * v 1 ) A force (F) causes a change in momentum F = M 1 * v 1 M 1 * v 2 = M 1 * (v 1 – v 2 ) = M 1 * a 1 When one body exerts a force on another then there is an equal an opposite reaction My F gravity = 80 kg * 9.8m/s 2 784 Newtons (or ~175 lbs)
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PYTS/ASTR 206 – Orbits and Gravity 9 Newton also figured out how to calculate the gravitational force between objects. Mass of object 1 (M
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1PTYS_206_orbits_gravity - PYTS/ASTR 206 Orbits and Gravity...

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