Earth – moon gravity primer
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Earth – moon gravity primer

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    Earth – moon gravity primer Earth – moon gravity primer Presentation Transcript

    • Earth – Moon Gravity Primer The Earth Sucks
    • 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).
    • Newton's Law of Universal Gravitation r m 1 m 2
    • 2. The Universal Gravitational Constant, G
    • 3. Gravity and Distance: The Inverse-Square Law
        • Gravity is the most dominant force in nature.
        • Yet it is the weakest.
    • Let’s look at the inverse-square nature for the force of gravity. 1 unit 2 units 3 units 4 units
    • 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.)
    • 5. OCEAN TIDES
        • demo - Earth-moon system
        • Force of gravity decreases with distance from moon.
      Moon Earth
      • 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
      • 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.
    • Sun Moon SFA
    • Sun Earth Spring Tides SFA New Moon Full Moon First Quarter
    • Sun Earth First Quarter Last Quarter Neap Tides SFA
    • NASA Animation MPEG SFA
      • Complications
        • Friction with ocean bottom
        • Irregular shape of continents
      • Bay of Fundi
        • Tides can come in very fast and exceed 15 m.
      SFA
    • 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
    • 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
    • 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
      • Objects accelerate in the direction of the arrows.
      • Field is stronger where lines are closer together.
      Earth SFA
    • The Gravitational Field Inside a Planet
      • Inside the Planet
      a = g a = g a = 0 a = ½g a = ½g SFA
    • Gravitational Field
      • Uniform Sphere
        • Linear inside - like Earth outside
      • Hollow Sphere
        • Zero inside - like Earth outside
      SFA
    • 7. EINSTEIN'S THEORY OF GRAVITATION
        • Warped Space
      SFA
    • Bending of Starlight Eye SFA Sun Light from star bent by the gravity of the Sun Apparent position of star in this direction
    • 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
    • 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
        • 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
    • Near a Black Hole SFA
    • Another Look SFA
    • 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!
    • Chapter 9 Review Questions
    • 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
    • What must be the phase of the moon if neap tides are occurring?
      • (a) first quarter
      • (b) full
      • (c) lunar eclipse
      • (d) new
    • 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
      • Discuss final
      • Parting thoughts next slide