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Astronomy Test Preparation: Newton's Laws and Rocket Physics

Join us tonight for a crucial 6-week test on Newton's Laws of Gravity and concepts in astronautics. The session runs from 7:15 to 8:30 PM in room 3425 Sterling, encompassing 55 multiple-choice questions. Expect a 2/3 focus on applying concepts and 1/3 on recall, covering all material discussed in lectures, discussions, and homework until Wednesday. Make sure to download the NASA article and review the reading materials related to gravity, orbital mechanics, and rocket physics. Prepare for an engaging learning experience!

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Astronomy Test Preparation: Newton's Laws and Rocket Physics

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  1. Bit of Administration …. • 6-Week Test • TONIGHT! 7:15-8:30, 3425 Sterling • 55 multiple choice questions • 2/3 conceptual use of the material • 1/3 recall • All material in lecture, discussion, homeworks through Wednesday; readings on that material • Reading • Download NASA article from www.astro.wisc.edu/astro104

  2. D Newton’s Law of Gravity 2 1 Fg Fg M1 = Mass of object 1 (grams) M2 = Mass of object 2 (grams) D = Distance between objects (cm) G = 6.67x10-8 cm3/sec2/gm

  3. Newton’s Law of Gravity Kepler’s 3rd Law In order for planet P to travel in a circle around the Sun… Central Force = Gravitational Force A P S Velocity depends only on distance, not on mass of planet Velocity decreases w. greater distance

  4. Newton’s Law of Gravity Kepler’s 3rd Law A P C

  5. Newton’s Law of Gravity Kepler’s 3rd Law In general, in units of cm, sec, gms For the Earth A P C 1 Solar Mass In general, in units of AU, years, solar masses For objects orbiting the Sun (Mc = 1 Mo)

  6. Nature and nature’s laws Lay hid in the night God said, “Let Newton be!” And all was light! - Alexander Pope

  7. Newton’s Law of Gravity Kepler’s 3rd Law - General Form for Mcentral >> Morbiting object A orb C P = Period of Orbit (years) A = Semi-Major Axis of Orbit (AU) Mc = Mass of central body (Solar Masses, Mo)

  8. Newton’s Law of Gravity Kepler’s 3rd Law - Weighing the Solar System Suppose a satellite is in orbit 8600 km above the Earth’s surface. Its period is 0.2 days. What is the mass of the Earth? A = 15,000 km = 10-4 AU (Earth radius is 6400 km) P = 0.2 days = 6 x 10-4 yr A

  9. Astronautics

  10. Astronautics

  11. Astronautics • What makes rockets go? • Newton’s 3rd Law

  12. Astronautics

  13. Astronautics • What makes rockets go? • Newton’s 3rd Law • Burn fuel to create hot gas • Allow gas to escape • Action of escaping gas => reaction of rocket motion • Important! The rocket does not push against anything - • this physics equally valid in the vacuum of space

  14. Astronautics • Before launch, the vast majority of mass to lifted is fuel!

  15. Astronautics

  16. Astronautics Launch Trajectory Atmosphere (not to scale) Earth

  17. Astronautics Launch Trajectory Earth Rotation 10,800 km/hr Earth

  18. Astronautics Launch Trajectory into Orbit 28,800 km/hr for orbit at Earth’s surface Earth Rotation 10,800 km/hr Earth

  19. ConcepTest! • In you were going to point in the direction that the Earth is rotating*, you would point • A) To the East • B) To the West • * Or put another way, the direction that you are moving right now because of the rotation of the Earth.

  20. Earth Rotation 10,800 km/hr Cape Canaveral

  21. Astronautics • Special Orbits Geosynchronous 36,000 km NP Low-Earth Orbit 200 km Mid-Earth Orbit 20,000 km

  22. ConcepTest! • In which orbit does a satellite have the longest period? • A) Low-Earth orbit • B) Mid-Earth orbit • C) Geo-synchronous orbit • D) Depends on the mass of the satellite

  23. Astronautics • Special Orbits Geosynchronous 36,000 km 24 hrs Weather, Surveillance NP Low-Earth Orbit 200 km 90 min Space Shuttle, Hubble Space Telescope Mid-Earth Orbit 20,000 km 12 hrs GPS, Communications

  24. ConcepTest! • In which orbit is a satellite moving faster? • A) Low-Earth orbit (Space Shuttle) • B) Mid-Earth orbit (GPS satellites) • C) Geo-synchronous orbit (Weather satellites) • D) Depends on the mass of the satellite

  25. Astronautics • Special Orbits Mid-Earth Polar Orbit 20,000 km 12 hrs Spy Satellites, GPS

  26. Earth Rotation 10,800 km/hr Cape Canaveral Vandenberg AFB

  27. ConcepTest! • If you are going to launch a satellite into a polar orbit from Vandenberg AFB, in which of these directions would you launch? • A) Southeast • B) South • C) Southwest • D) West

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