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Std. IE 1k- Students will recognize the cumulative nature of scientific evidence Objective 1: Compare models of the solar systems Objective 2: Summarize Kepler’s three laws of planetary motion Objective 3: Describe how Newton explained Kepler’s laws of motion

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Geocentric – Earth centered model (Aristotle) the sun, stars, and planets revolve around the Earth Did not explain retrograde motion - the appearance of some planets moving backward

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Epicycles – small circle movements (Ptolemy) Heliocentric model - the sun the center (Nicolaus Copernicus)

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What is the geocentric model? Earth centered model What is the heliocentric model? Sun centered model What is the movement of planets in small circles? Epicycles What is the appearance of planets moving backward in the sky? Retrograde motion

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Johannes Kepler discovered patterns which led him to develop 3 laws that explained planetary motion 1) Law of Ellipses 2) Law of Equal Areas 3) Law of Period

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1 st law - States that each planet orbits the sun in a path called an ellipse (not a circle ) Elliptical orbits can vary in shape (elongated or circles) Eccentricity – the degree of elongation of an elliptical orbit

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2 nd law - states that equal areas are covered in equal amounts of time as an object orbits the sun It describes the speed at which objects travel at different points in their orbits Ex. Mars moves fastest in its elliptical orbit when it is closest to the sun

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3 rd law – states the relationship between the average distance of a planet from the sun & the orbital period of the planet Scientist can find out how far away the planets are from the sun by using this law Orbital Period - the time required for a body to complete a single orbit

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Which of Kepler’s laws states that equal areas are covered in equal amounts of time? 2 nd law – Law of Equal Area Which of Kepler’s laws states that each planet orbits the sun in a path called an ellipse? Law of Ellipses What is the time required for a body to complete a single orbit? Orbital Period

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Newton used inertia to help explain Kepler’s laws. Inertia - a moving body will remain in motion and resist a change in speed or direction until an outside force acts on it

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Planets do not follow a straight path Gravity = an outside force that cause the orbit to curve Gravity exists between any two objects in the universe Formation of curved orbits 1. Gravitational pull sun pulls objects towards it 2. Inertia keeps the object moving in a straight line

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What exists between any 2 objects in the universe? Gravity What is a body remaining in motion unless acted on by an outside force called? Inertia What is pulling the planets toward the sun? Gravity What gives planets their curved orbits? Inertia and gravitational pull

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