Physics

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Physics

• How the universe works!

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Isaac Newton

• 1642 1727 AD

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Traveling out into space

• Suppose that you are in a spaceship traveling
  past two different planets. You pass a blue
  planet that has twice the mass of the Earth at a
  distance of 1 AU, then you pass a red planet that
  has the same mass as the Earth, also at a
  distance of 1 AU. From which planet will you
  feel the greater gravitational pull?
• a. the blue planet
• b. the red planet
• c. neither the gravitational pull from
• each planet will be equal

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Still traveling

• Suppose that you are in a spaceship traveling
  past two different planets. You pass a blue
  planet that has the same mass as the Earth at a
  distance of 1 AU, then you pass a red planet that
  also has the same mass as the Earth, but at a
  distance of 2 AU. From which planet will you
  feel the greater gravitational pull?
• a. the blue planet
• b. the red planet
• c. neither the gravitational pull from
• each planet will be equal

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Almost home

• Compared to your mass here on Earth, your mass
  out in space between the stars would be
• a. zero.
• b. negligibly small.
• c. the same.
• d. unknown.

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GRAVITY
G M1 M2
F
R2
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Johannes Kepler

• From
• to three Laws of Planetary Motion in 10 years
  and thousands of pages of calculations!

http//www.pafko.com/tycho/observe.html

• 1571 1630 AD

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Keplers First Law

• Orbits are

• Orbits are ellipses with the Sun at one focus.

http//www.daviddarling.info/encyclopedia/E/ellips
e.html
http//www.math.rutgers.edu/courses/251/maple_new/
maple3.html
Eccentricity Simulator
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Earths elliptical orbit

• The Earths orbit is slightly elliptical at its
  perihelion it is approximately 147 million km
  from the Sun, and at aphelion it is approximately
  152 million km from the Sun. Which of the
  following is a result of the Earths elliptical
  orbit?
• a. It is summertime at perihelion and
• wintertime at aphelion.
• b. The Earth moves faster in its orbit at
• perihelion and slower at aphelion.
• c. Days are longer at aphelion and shorter
  
• at perihelion.
• d. The Earth spins faster at perihelion and
• slower at aphelion.

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Keplers Second Law

• Equal areas in equal times An imaginary
  straight line between a planet and the Sun sweeps
  out equal areas in equal times as the planet
  moves around the Sun.

http//observe.arc.nasa.gov/nasa/education/referen
ce/orbits/orbit2.html
Simulation of Keplers 2nd Law
http//astro.unl.edu/naap/pos/pos_background1.html
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Keplers Third Law

• The square of a planets orbital period is
  proportional to the cube of its semimajor axis.

http//jersey.uoregon.edu/kepler/Kepler.html
Simulation of Keplers 3rd Law
Additional Keplers 3rd Law Simulation
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Kepler developed these laws for planets,
but

• they work for any object orbiting around another!

http//outreach.atnf.csiro.au/education/senior/ast
rophysics/binary_intro.html
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Simulated orbits
http//en.wikipedia.org/wiki/Center_of_mass
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Guiding Questions

• What quantities determine the force of gravity
  between two objects?
• Using Newtons Law of Gravity, describe how the
  force of gravity varies based on objects masses
  and distance from one another.
• Describe what Keplers Laws tell us about the
  motions of planets in our solar system.
• What makes an ellipse different from a random
  oval?
• Explain how Keplers 2nd and 3rd Laws are
  different.
• How does gravity explain Keplers 2nd and 3rd
  Laws?