Gravity and Motion Continued Orbital Motion Why do

Gravity and Motion Continued

Orbital Motion • Why do the Earth and Moon remain in orbit? • Newton concluded that inertia and gravity combine to keep the Earth in orbit around the sun and the moon in orbit around the Earth. • Look at figure 2 on page 106

Gravity and Inertia

How Does Gravity Help Form Planets, Stars, and Solar Systems? • How do things in space form? • Scientist think that gravity helps form solar systems by bringing material together in a gradual buildup. • Accretion- the process of building something up gradually by the gathering together of smaller pieces

How Does Gravity Help Form Planets, Stars, and Solar Systems? • Read 2 nd paragraph on page 108

Gravity Forms Solar Systems • Scientists think that all solar systems begin as clouds of material • The clouds include: hydrogen, helium, rock, ice, and other material • The law of universal gravitation says- every object in the universe attracts every other object in the universe • For a solar system to form gravity must pull the cloud material together • As the cloud collapses and starts to rotate it forms a spinning disk

Gravity Forms Stars • Most of the material in the spinning disk is pulled to the center • The material becomes tightly packed as it undergoes accretion • It gets hotter and the pressure increases • Eventually is gets so high that the hydrogen atoms will bond together to form helium • This process is called nuclear fusion (this is what gives off the light and heat)

Gravity Forms Planets • Some of the material in the spinning disk remains outside the star and forms the planets • Gravity pulls rock, ice, and gas together • Rock and ice will collide forming small bodies which will combine to others and create planets and other bodies in our solar system (asteroids and comets)

Gravity Keeps Solar Systems Together • Why don’t planets and stars fly away into space? • The star at the center of the solar system exerts a large gravitational force on all the other objects in the solar system • The gravity of the star keeps the other objects from flying away so they stay in orbit

How the Solar System Formed