1. Laws of Planetary Motion KEPLER & NEWTON

2. Kepler’s 3 Laws  1 st Law- Law of Ellipses  2 nd Law- Law of Equal Areas  3 rd Law- Law of Periods

3. 1 st Law- The Law of Ellipses  The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus.  Ellipse= oval shape, NOT circular  Shape is determined by 2 points called foci within the ellipse  One focus is in the Sun, No object in 2 nd focus  Shape can vary  Elongated or almost perfect circles  Eccentricity = degree of elongation of the ellipse (how big the shape is)

4. Law of Ellipses

5. 2 nd Law- The Law of Equal Areas  Planets move at different speeds at different points in their orbit around the Sun  Perihelion= point when an object is closest to the Sun in orbit  Aphelion= point when an object is furthest from the Sun in orbit

6. The Law of Equal Areas  Object is closer to the sun = moves faster  Object is further from the sun = moves slower

7. 3 rd Law- The Law of Periods  There is a relationship between the distance from the Sun and the time for orbital period of a planet  Period= revolution around the Sun  Allows scientists to determine how far away the planets are from the Sun by measuring the time it takes a planet to orbit the Sun  farther away = long time to orbit  Close to the Sun = short time to orbit

8. Newton’s Law of Universal Gravity  Gravity: the force that attracts a body toward the center of the earth, or toward any other physical body having mass.  Amount of gravity is directly proportional to their mass  More Mass = More Gravity  Less Mass = Less Gravity  Gravitational force exists between any 2 objects in the Universe  Sun’s gravity holds planets in orbit  Far away from the Sun = less gravitational pull on planet  Close to the Sun = More gravitational pull on planet  Smaller objects are pulled closer and larger objects are further away  Inner Planets = small; close to Sun  Outer planets = Large; far from Sun

9. Newton’s Law of Inertia  An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.unless acted upon by an unbalanced force  Inertia keeps objects moving forward in a straight line unless stopped by something else  Inertia and Gravity keep planets moving in an elliptical orbit