1. Solar System Physics Astronomy 311 Professor Lee Carkner Lecture 6

2. How does Newton’s First Law explain why planets do not fall into the Sun? a)Gravity holds them in place b)The action of gravity causes an opposite reaction that opposes gravity c)The planets are rotating on their axis and angular momentum must be conserved d)The planets have inertia and want to keep moving along their orbits e)It doesn’t, only Kepler’s Laws do

3. If the force on an object and the mass of an object are both doubled, what happens to the acceleration? a)It is ¼ what is was before b)It is ½ what it was before c)It is the same as what it was before d)It is 2 times what it was before e)It is 4 times what it was before

4. Notes  Quiz #1 is next Monday (Sept 15)  Short answer and multiple choice  Covers lectures 1-8 (through “Origin of the Solar System”)

5. Physics and the Solar System  There are many physical effects that are important in shaping the solar system  We will concentrate on three:    Impacts (when we talk about Mercury)

6. Newton’s Law of Universal Gravitation  Gravity -- a force that all objects exert on each other proportional to their mass and inversely proportional to the distance squared F=Gm 1 m 2 /r 2   multiply distance by 2, decrease force by 2 squared (4) 

7. Using The Gravity Equation   G = 6.67 X 10 -11  in units of (N m 2 /kg 2 )   One newton is the force the Earth exerts on a ¼ pound object on its surface

8. Tides   Example: Tides on the Earth   Moon pulls the center away from the far side  The tidal force tries to stretch the Earth into a football shape  This mostly effects the oceans

9. High and Low Tide

10. Types of Tides   The actual amount the water level changes is strongly dependant on geography and location  Sun also produces tides   Spring Tide -- Sun and Moon pulling together, strongest tides  Neap Tide -- Sun and Moon pulling against each other, lowest tides

11. Spring and Neap Tides

12. Synchronous Rotation   The moon is tidally locked   The Earth’s gravity distorts the Moon, slowing its rotation  Tidal bulge wants to be pointed at the Earth

13. Evaluating a Theory  Use the scientific method in detail   Use scientific reasoning    Rely on others who use the scientific method 

14. Scientific Notation   e.g., 630000000000.0 = 6.3 X 10 11   e.g. “6.3EE 11 ”  n.b., not “e”, “10 x ”, or “y x ”  Always write on your paper as exponential  Also note, 6.3 X 10 11 ≠ 6.3 11

15. Magnetic Fields   A magnetic field exerts a force on charged particles  Can manifest itself via:    Acceleration

16. Magnetic Field Generation   The dynamo effect requires that a planet have a liquid, conducting interior  Like the molten iron in the Earth   Currents produce magnetic fields  Like an electromagnet  Magnetic fields are dipolar

17. Earth’s Magnetic Field

18. Solar Wind   Ions are missing electrons and so have a net charge   Sun’s magnetic field produces the solar wind, planet’s magnetic field deflects and traps the solar wind

19. Magnetosphere  A planet’s magnetic field interacts with the solar wind to produce a magnetosphere   Particles from wind get trapped in magnetic field   Size of magnetosphere changes as solar wind ebbs and flows

20. The Earth’s Magnetosphere

21. Charged Particle Belts  All planets with magnetic field have particle belts   The interaction of the particles and the magnetic fields produce currents   The moving particles collide with molecules in the atmosphere exciting them and producing light 

22. Next Time  Read Chapter 5 and 6.6

23. Summary  Physics  Gravity, impacts and magnetic fields are responsible for a wide range of solar system phenomena  Gravity  All solar system bodies effect each other gravitationally, but the effect is often small  Strong gravitational fields produce tides  Differential gravity creates bulges on opposite sides of a planet

24. Summary  Magnetic fields  liquid interior allows moving charges to generate field via dynamo  magnetosphere deflects solar wind (deflection)  magnetosphere traps solar wind charged particles (trapping)  magnetosphere creates currents of solar wind charged particles (acceleration)