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# Ch. 3 Section 3

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## Jemma Sabokrouh

on 11 January 2015

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#### Transcript of Ch. 3 Section 3

What Determines Gravity?
Earth revolves around the sun in a nearly circular orbit.
orbit: the path of an object as it revolves around another object in space.
Gravity
Gravity is what keeps the earth in orbit.
The Law of Universal Gravitation states that every object in the universe attracts every other object
*** The strength of the force of gravity between 2 objects depends on 2 factors: Their masses and the distance between them!
Mass is the amount of matter in an object
NOT TO BE CONFUSED WITH...
Weight- the force of gravity on an object
Which one changes based on your location?
An object with less mass will feel less gravitational pull from the sun.
So...if the sun is pulling the earth toward itself, why doesn't the earth go into the sun??
Ch. 3 Section 3
Gravity and Motion

Why doesn't the earth fly off into space???
Isaac Newton realized that there must be a force acting on the earth and the moon, and the sun and the earth that keep them in orbit.
Force: A push or pull
Weight!!
*on the moon you

Likewise, when two objects are farther apart from each other, the force of gravity between them is less.
Intertia.
Inertia is the tendency of an object to resist a change in motion.
Newton's 1st Law of Motion
says that an object in motion
tends to stay in motion and an object at rest tends
to stay at rest.
Orbital Motion
Newton concluded that a combination of gravity and intertia is what keeps objects like earth and the moon in orbit!
http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g46/
see simulation**
http://www.pbslearningmedia.org/resource/ess05.sci.ess.eiu.moonorbit/why-doesnt-the-moon-fall-down/?utm_source=teachersdomain_redirect%2Fresource%2Fess05.sci.ess.eiu.moonorbit%2Futm_medium%3Dteachersdomain%2Fresource%2Fess05.sci.ess.eiu.moonorbit%2Futm_campaign%3Dtd_redirects
Gravity and the Formation of Celestial Bodies
Gravity plays a big role in the formation of planets, stars, and solar systems!
Gravity helps form solar systems by bringing material together in a gradual buildup.
This process of building something up gradually by gathering small pieces together is called ACCRETION
http://www.sciencechannel.com/video-topics/space-videos/the-planets-different-worlds-accretion.htm
Forming the Solar Systems
1. Huge cloud of dust and materials
2. Due to the law of universal gravitation, all these materials are attracted to each other.
3. Materials pull together due to gravity
4. The gathered materials start to rotate and form a spinning disk
Forming Stars
Most of the material from the spinning disk is pulled to the center
The materials become very tightly packed as accretion continues to occur
The mass gets hotter and the pressure increases
Eventually pressure gets so high that hydrogen atoms fuse to form helium-- Nuclear fusion!
Nuclear fusion causes the star to release energy once it has formed, giving off heat and light
Forming Planets
The leftover materials form the original spinning disk stay outside of the newly formed star.
Accretion continues to occur with these leftovers
Chunks of rock and ice and gas are pulled together by gravity and eventually form small bodies--planets.
Keeping it Together
What keeps all the objects in the solar system from flying off into space?
GRAVITY of course!
Since the sun is so large compared to the planets, the gravitational force it exerts on the planets keeps them in orbit