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**Law of universal gravitation**

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**Misconceptions about falling objects video **

(Veritasium) Video from the universe beginning (TED)

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**Lesson 1 Focus questions**

What do we mean when we say gravity is always an “attractive” force? What is G? Why is the law of universal gravitation called an “inverse square law” Is gravity a field or contact force? Handout: Planetary Data Sheet (NASA)

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**Notes- Law of Universal Gravitation**

Any two masses are gravitationally attracted to each other Newton’s Law of Universal gravitation: Fg = G m1 m G= 6.673x10-11N•m2 r kg2 r is the distance from the center of one object to the center of the other r m1 m2

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**Notes- Law of universal grav.**

As the distance r between the objects increase what happens to the force? ________ If mass increases and the distance between the objects stays the same, how does this affect the force? ____________ Sooooo.. the closer the objects the ________ the more massive the objects the ______

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**Notes- Law of universal grav.**

As the distance r between the objects increase what happens to the force? decreases If mass increases and the distance between the objects stays the same, how does this affect the force? increases Sooooo.. the closer the objects the greater the force the more massive the objects the the greater the force

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Notes Example…… What is the gravitational force of attraction between Pluto and the sun? Note: masspluto = x 1022 kg mass sun = x1030 kg r pluto-sun= x 109 m

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**Applying Newton’s Law of Universal gravitation- example**

Two students are 5.0m apart. One has a mass of 35kg, the other has a mass of 70 kg. What is the force of gravity from one student on the other?

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Now you try Calculate gravity on the surface of the Earth.

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**Circular Motion- The Big Idea**

Big idea: to maintain circular motion requires a force directed inward. This is caused by gravity (for planets)

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Putting it all togher!!! From the last unit we learned to maintain circular motion you need an inward directed force . IN THE CASE OF A PLANET ORBITING THE SUN THAT INWARD DIRECTED FORCE IS THE FORCE OF GRAVITY!!!!!!! orbital motion: Fc = Fg So mv2 = Gm1m2 r r2

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Worksheet In small groups work on the worksheet showing your steps to proper problem solving, boxing answers and including appropriate units!

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