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Earth – moon gravity primer

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  • 1. Earth – Moon Gravity Primer The Earth Sucks
  • 2. 1. THE UNIVERSAL LAW OF GRAVITY
      • From Law 3 of Kepler, Newton deduced the inverse square law of attraction.
      • Newton compared the fall of the moon to the falling of an apple.
      • Moon's fall from straight line is (0.05 in/s).
  • 3. Newton's Law of Universal Gravitation r m 1 m 2
  • 4. 2. The Universal Gravitational Constant, G
  • 5. 3. Gravity and Distance: The Inverse-Square Law
      • Gravity is the most dominant force in nature.
      • Yet it is the weakest.
  • 6. Let’s look at the inverse-square nature for the force of gravity. 1 unit 2 units 3 units 4 units
  • 7. 4. WEIGHT AND WEIGHTLESSNESS
      • W = mg (the gravitational force acting on m)
      • Weighing on an elevator and
      • Weighing in outer space or in orbit
      • We define the weight of something as the force it exerts against the supporting floor or the weighing scale. (Remember the elevator video.)
  • 8. 5. OCEAN TIDES
      • demo - Earth-moon system
      • Force of gravity decreases with distance from moon.
    Moon Earth
  • 9.
    • Differences in gravity on different parts of the Earth produce tidal bulges.
    • http://www.spacetelescope.org/videos/html/mpeg/320px/heic0705i.html
    High Tides North Pole
  • 10.
    • Should expect two high tides, two low tides per day.
      • Moon moves in its orbit so that it returns to the same place in your sky every 24 h 50 m .
    • Sun has one-half the influence of the moon
      • The gravitational force is greater but tides depend on the gravitation difference on opposite sides of the Earth.
  • 11. Sun Moon SFA
  • 12. Sun Earth Spring Tides SFA New Moon Full Moon First Quarter
  • 13. Sun Earth First Quarter Last Quarter Neap Tides SFA
  • 14. NASA Animation MPEG SFA
  • 15.
    • Complications
      • Friction with ocean bottom
      • Irregular shape of continents
    • Bay of Fundi
      • Tides can come in very fast and exceed 15 m.
    SFA
  • 16. Tides in the Earth and Atmosphere
    • Tides in ionosphere produce electric currents and alter the magnetic field.
      • Affects penetration of cosmic rays
      • Can have effects on living things
    • Tides in the crust mean that volcanoes and earthquakes are more common at new or full moon.
    SFA
  • 17. Tides on the Moon
    • Just as the earth has “land tides” the moon has moon tides.
    • Because the moon always keeps the same face toward the earth, the moon tides are always in the same place.
    SFA Go to link
  • 18. 6. GRAVITATIONAL FIELDS
    • Alternate view of gravitational influence
      • Properties of space surrounding object are changed so that another mass entering the region experiences a force.
    Earth SFA
  • 19.
    • Objects accelerate in the direction of the arrows.
    • Field is stronger where lines are closer together.
    Earth SFA
  • 20. The Gravitational Field Inside a Planet
    • Inside the Planet
    a = g a = g a = 0 a = ½g a = ½g SFA
  • 21. Gravitational Field
    • Uniform Sphere
      • Linear inside - like Earth outside
    • Hollow Sphere
      • Zero inside - like Earth outside
    SFA
  • 22. 7. EINSTEIN'S THEORY OF GRAVITATION
      • Warped Space
    SFA
  • 23. Bending of Starlight Eye SFA Sun Light from star bent by the gravity of the Sun Apparent position of star in this direction
  • 24. 8. BLACK HOLES
      • Let’s observe a star that is shrinking but whose mass is remaining the same.
      • What happens to the force acting on an indestructible mass at the surface of the star?
      • What effect is there on the escape velocity?
    SFA
  • 25. R R R R Remember that the force between the two masses is given by SFA R 2 F R 2 F R 2 F R 2 F which means the force is 64 times larger
  • 26.
      • If a massive star shrinks enough so that the escape velocity is equal to or greater than the speed of light, then it has become a black hole.
      • Particles entering it would suffer disintegration.
      • How are black holes detected?
    SFA
  • 27. Near a Black Hole SFA
  • 28. Another Look SFA
  • 29. 9. UNIVERSAL GRAVITATION
      • Earth is a "sphere" because of gravitation.
      • The universal law of gravitation was a great accomplishment.
      • Its accuracy is phenomenal.
      • Perturbations in planet's orbits
      • Examples:
      • Neptune was discovered because of Uranus's wobble.
      • Pluto was discovered in a similar way.
      • Oscillating universe. Wow!
  • 30. Chapter 9 Review Questions
  • 31. If somehow the moon were moved to a distance twice as far away from the earth as it is now, the force that the earth has for the moon would
    • (a) be twice what it is now
    • (b) be one half of what it is now
    • (c) be four times greater than it is now
    • (d) be one fourth as much as it is now
  • 32. What must be the phase of the moon if neap tides are occurring?
    • (a) first quarter
    • (b) full
    • (c) lunar eclipse
    • (d) new
  • 33. Newton said that the path of a planet curves because a force acts on it. Why does a planet's path curve according to Einstein?
    • (a) because a force acts on it
    • (b) because it is spinning
    • (c) because it is in a geometric warp of space and time
    End of Course End of Chapter Test 3 Questions
  • 34.
    • Discuss final
    • Parting thoughts next slide