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a little physics
SESAME Astronomy Winter 2011week 2
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helpful concepts
mass
gravity
angular momentum
atoms
heat/energy/temperature
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mass
“stuff”
matter
inertia
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Gravityforce between 2 objects with mass
always attractive
increases with increasing mass
decreases with increasing distance between objects
Force of gravity = a constant x(distance between objects)2
(mass of object 1) x (mass of object 2)
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Gravity is responsible for...Keeping us grounded
Keeping the moon in its orbit around Earth
Keeping the planets (and asteroids) in their orbit around the sun
Keeping the sun in its orbit around the Milky Way
making comets fall in toward inner solar system
making gas clouds collapse into stars and planets
Putting Andromeda and the Milky Way on a collision course
Making us fall into the local Supercluster
creating the anisotropies in the cosmic microwave background
keeping stars together so they can burn (instead of blowing apart from their heat
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(see ch 5 cannon ball applet)
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angular momentum
moment of inertia x angular speed (how fast it’s turning)
it’s conserved
big and spinning slowly = small and spinning quickly
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atoms
building blocks of matter
smallest unit of an element that still has properties of that elements
made of protons, neutrons, and electrons
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atomsdifferent elements have different numbers of protons (and neutrons, and electrons)
1 atomic mass unit (amu) = mass of 1 proton (or neutron)
ignore electron’s mass (1/1700 amu)
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atomsprotons -> positive charge
neutrons -> no charge
electrons -> negative charge
nucleus (center)
protons and neutrons
where most of mass is
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energyKinetic energy
energy of motion
1/2 x mass x (speed)2
1/2 m v2
Potential energy
•has the potential to have kinetic energy
equation depends on what’s generating PE
gravitational PE on surface of Earth: mass x constant x height
general gravitiational PE:
(sigh)
(mass of object 1) x (mass of object 2)distance between objects
PE = a constant x
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energy
imagine a bowling ball and a golf ball moving at the same speed. which one has higher kinetic energy?
imagine a bowling ball and a golf ball with the same kinetic energy. which one is moving faster?
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energy
imagine a Hydrogen atom (1 proton, 0 neutrons) and a Carbon atom (6 protons, 6 neutrons) at the same temperature. which one is moving faster?
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energy
conserved (KE + PE = constant)
Example: sun and planet
1/2 mplanet v2 + G (msun mplanet)/d = constant
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energy + atoms = temperature
Temperature = Kinetic Energy of atoms
comparisons:
at a given T, are more massive atoms are moving faster or slower?
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energy + atoms + gravity + angular momentum
= Solar System formation
imagine a gas cloud (mostly Hydrogen, some Helium, a little Carbon, Oxygen, Nitrogen, Iron...)
it’s rotating slightly
gravity pulls the atoms in - makes it collapse
as the cloud contracts,
as atoms move , temperature
Yay!what happens to the speed of
its atoms?the atoms move faster
faster increases
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energy + atoms + gravity + angular momentum
= Solar System formation
some of the atoms stick together - now they have more mass, so they attract more atoms, which gives them more mass, and planets form
the center of the cloud is the densest hottest part, and it gets so hot that fusion starts in the center - a star is born!
we’ll get to fusion when we cover stars, or at least, the sun
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energy + atoms + gravity + angular momentum
= Solar System formation
closer than a certain distance, just inside the orbit of Jupiter, the temperature is relatively high, so light elements (Hydrogen and Helium) can escape
same T, lower, mass -> higher speed (in fact, escape speed) -> rocky (terrestrial) planets
Farther out, the light elements can’t escape/evaporate, so they get accreted onto the planets -> gas (jovian) planets
smaller rocky planets in inner Solar System, larger gas planets in outer Solar System
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ch 9collapse of solar nebula (with and without skater),formation of protoplanetary diskwhy does the disk flattenaccretion and formation of planets,condensate regionscomparative planetology
ch 8: kepler_3_orbit...htm