Notes
No class Monday (Sept 5) Quiz #1 is the next Monday (Sept
12) Short answer and multiple choice Covers lectures 1-8 (through “Origin
of the Solar System”)
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)
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=Gm1m2/r2
multiply distance by 2, decrease force
by 2 squared (4)
Using The Gravity Equation
G = 6.67 X 10-11 in units of (N m2/kg2)
One Newton is the force the Earth
exerts on a ~¼ pound object on its surface
Evaluating a Theory
Use the scientific method in detail
Use scientific reasoning
Rely on others who use the scientific method
Scientific Notation
e.g., 630000000000.0 = 6.3 X 1011
e.g., “6.3EE11” n.b., not “e”, “10x”, or “yx”
Always write on your paper using “X10” Also note, 6.3 X 1011 ≠ 6.311
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
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
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
Magnetic Fields
A magnetic field exerts a force on charged particles
Can manifest itself via: Acceleration
Magnetic Field Generation
The dynamo effect requires: liquid interior conducting interior reasonably fast rotation
As the liquid moves around, it carries ions
with it, producing a current Like an electromagnet
Magnetic fields are dipolar
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
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
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
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
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