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# 9.4 - Orbital Motion & Kepler's third law

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### 9.4 - Orbital Motion & Kepler's third law

1. 1. 9.4 – Orbital Motion & Kepler’s 3rd Law
2. 2. Orbital Motion in the Solar System
3. 3. Kepler’s LawsIn the early 1600s Kepler summarized the carefullycollected data of Tycho Brahe and proposed three laws:1st Law: The Law of ellipsesThis just said that planets moved inellipses around the sun.The ends and length of the string in the picture isfixed and the pencil draws out an ellipse.2nd Law: The Law of equal areasThe area swept out by the orbit in acertain time is constant. You don’t need to know these, only the 3rd Law!
4. 4. 3rd Law: Time Period and Radius of orbit relationship Use this simulation link to investigate Kepler’s Third Law: http://bit.ly/keplers3rdlaw or CLICK ON THE PICTURE
5. 5. LearnDerivation of Kepler’s 3rd Law This!!When something is in orbit, Centripetal Force is caused by Gravitational Force. +The 3rd Law: The square of theorbital period of a planet isdirectly proportional to thecube of the semi-major axis ofits orbit
6. 6. LearnEnergy of an orbiting body - derivations This!! 1. Remember: and 2. Remember for objects in orbit: FC = FG Centripetal Gravitational Force Force KE
7. 7. Graphs of KE, PE and Total Energy
8. 8. Graphs of KE, PE and Total Energy
9. 9. Graphs of KE, PE and Total Energy
10. 10. Energy, Orbits & Escape SpeedTry these two simulations to help your understanding:1. Energy & Orbits 2. Energy & Escape Speedhttp://webphysics.davidson.edu/physlet_res http://webphysics.davidson.edu/physlet_resources/bu_semester1/c17_orbits.html ources/bu_semester1/c17_escape.html BLUE = KE PINK = PE BLACK = Total Energy
11. 11. Weightlessness What’s happening? What happened to gravity?
12. 12. Weightlessness The plane follows a strange parabolic flight path that gives about 30 seconds of weightlessness
13. 13. Weightlessness If everything is accelerating downwards at the same rate then we get the illusion of weightlessness. Because the space station is orbiting the earth, everything in it is being accelerated towards the centre of the earth. This is what happens with all circular motion.