CHAPTER 27.2 MODELS OF THE SOLAR SYSTEM

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

Models of the Solar System

Geocentric – Earth centered model (Aristotle) the sun, stars, and planets revolve around the

EarthDid not explain retrograde motion - the

appearance of some planets moving backward

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

(Nicolaus Copernicus)

Objective 1: Compare models of the solar systems

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

Kepler’s Laws

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

1) Law of Ellipses

1st 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

2) Law of Equal Areas

2nd 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

3) Law of Periods

3rd 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

Objective 2: Summarize Kepler’s three laws of planetary motion

Which of Kepler’s laws states that equal areas are covered in equal amounts of time? 2nd 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

Newton’s Explanation of Kepler’s Law

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

Newton’s Models of Orbits

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

Objective 3: Describe how Newton explained Kepler’s laws of motion

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