AST 101 Exam 2 Laws of Astrophysics

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Keplers 1st Law (Orbital Motion)
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Planets travel in elliptical orbits with the sun as a focus
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Keplers 2nd Law (Orbital Motion)
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The line going from the Sun to the planet sweeps out equal areas in equal times *Explains relationship between planets around the sun
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Keplers 3rd Law (Orbital Motion)
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The time that a planet takes to go around the sun increases as the 3/2 power of the long axis of the ellipse T^2=A^3
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Newton- astrophysics
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Applies physical laws discovered on Earth to phenomena in cosmos
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Newton’s 1st Law (Motion)
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An object moves at a constant velocity unless a net force acts to change its speed/direction *In the absence of a net force and object will move with constant velocity
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Newtons 2nd Law (Motion)
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Net force will change an objects momentum, accelerating it in the direction of the force *2nd law states: The amount of acceleration depends on the object’s mass and the strength of the net force Force= mass x acceleration “F=ma”
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How does earth manage to keep rotating and going around the sun day after day, year after year?
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ANGULAR MOMENTUM- Special type of momentum that we use to describe objects turning in turning in circles/going around curves
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Law of conservation of angular momentum
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An individual object can change its angular momentum only by transferring some angular momentum to or from another object–> Total angular momentum can never change Angular Momentum= Mass x Velocity x Radius
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Newton’s 3rd Law (Motion)
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Every Force is paired with an equal and opposite reaction force *Scenario: Standing on pavement…you are not sinking. No net force acting on you that percisely offsets the downward force you exert on the ground
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Newton’s Law of Universal Gravitation
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Any two masses attract each other with a force equal to a constant (constant of gravitation) multiplied by the product of two masses and divided by the square distance between them

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