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March 28 - Do NOW - - Take your clickers, and write this down and solve in your notes: Action: Earth pulls moon. - What is the reaction? - What is stronger – action, reaction, or same? - What Law defends your answer?

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**Action: Earth pulls moon. What is the reaction?**

Sun Pulls Earth Moon pulls Earth Sun pulls moon No reaction

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**Action: Earth pulls moon. What is stronger – action, reaction, or same?**

Reaction (moon pulls Earth) Same!

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**What law defends your answer?**

1st Law 2nd Law 3rd Law

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PHET Computer Lab 15 minutes to complete the entire packet – go!

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**Lab Review Clickers ready! We are not reviewing individual questions…**

Rather, we are reviewing MAIN CONCEPTS Feel free to take note/ make corrections on your lab OR write stuff down…but work fast!!! We are rapidly completing!

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**Choose the picture you think shows the gravity forces on the Earth and the Sun.**

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**How would these gravity forces change if the Sun got more massive?**

Increase Decrease Stay the same

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**How would these gravity forces change if the Earth was much closer to the Sun?**

Increase Decrease Stay the same

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**How would these gravity forces change if the Earth got much less massive?**

Increase Decrease Stay the same

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**How would these gravity forces change if the Earth and Sun were moved farther apart?**

Increase Decrease Stay the same

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**The force of gravity increases as objects move closer together.**

True False

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**The force of gravity increases as an object’s mass increases. **

True False

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** If two objects have different masses, the more massive object pulls with a greater force. **

True False

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An object with more mass is able to exert more gravitational force than an object with a smaller mass. True False

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**Based on those last questions…**

Think about PROPORTIONS between… MASS and FORCE DISTANCE and FORCE Are they directly or inversely proportional?

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**What is the relationship between mass and force?**

Directly proportional Inversely proportional

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**What is the relationship between distance and force?**

Directly proportional Inversely proportional

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**Gravitational force is always attractive / repulsive. **

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**Gravitational force exists everywhere / only in some places in the universe **

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IF a gravitational force exists between two objects, one very massive and one less massive, then the force on the less massive object will be greater than/ equal to / less than the force on the more massive object. greater than Less than Equal to

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**As the distance between masses decreases, force increases / decreases. **

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12.3 The Falling Earth What would happen to the paths of the planets if GRAVITY was reduced to zero? Would they… Continue to orbit the sun as usual? Crash straight into the sun? Take the tangent path away from the sun? Use what you know about forces and circular motion to DEFEND your answer using scientific reasoning

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**What would happen if the paths of the planets if GRAVITY was reduced to zero?**

Continue to orbit the sun as usual Crash straight into the sun Take the tangent path away from the sun?

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12.3 The Falling Earth What would happen if the paths of the planets if GRAVITY was reduced to zero? Their motion would be TANGENT, away from the sun and they would stop orbiting it. All objects in the solar system have long ago taken on some kind of rotation or revolution (result of the Big Bang)…because GRAVITY was one of the first things to emerge from the Big Bang, and GRAVITY provides the centripetal force on planets, moons, etc.!

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**Choose the picture of how the Earth would move if you “turned off” the gravity forces.**

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**Take out your HW… #1-7 (Ch 12) Checking now with clickers**

Checking later with peers

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**#1 –Why did Newton think there must be a force acting on the moon?**

It moved in a straight line, not a circle It moved in a circle, not a straight line I had no clue how to answer this question

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#2 What did Newton conclude about the force that pulls apples to the ground and the force that holds the moon orbit? They were different forces They were the same force I had no clue how to answer this question

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**#3 If the moon falls, why doesn’t it get closer to Earth?**

It has a large tangential speed, so it falls around Earth and not into it It has a small tangential speed, so it falls around Earth and not into it I had no clue how to answer this question

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#4 What is meant by tangential speed? Check with your neighbor

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#5 How did Newton check his hypothesis that there is an attractive force between Earth and moon? Check with your neighbor …

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**#6 What is required before a hypothesis can become a theory?**

Check with your neighbor

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**#6 What is required before a hypothesis can become a theory?**

Check with your neighbor …

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**#7 Since there is gravity between the planets and the sun, why don’t the planets crash into the sun?**

They have small tangential speeds, so they fall around sun and not into it They have large tangential speeds, so they fall around sun and not into it I had no clue how to answer this question

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**#7 continued… What would happen to the tangential velocities of the planets were reduced to zero?**

Would they… Continue to orbit the sun as usual? Crash straight into the sun? Take the tangent path away from the sun? Use what you know about forces and circular motion to DEFEND your answer using scientific reasoning

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**What would happen if the tangential velocities of the planets were reduced to zero?**

Continue to orbit the sun as usual Crash straight into the sun Take the tangent path away from the sun?

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12.3 The Falling Earth What would happen if the tangential velocities of the planets were reduced to zero? Their motion would be straight toward the sun and they would indeed crash into it. Any objects in the solar system with insufficient tangential velocities have long ago crashed into the sun. (Same concept applies to the moons and other objects orbiting planets!!)

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Which picture would show the path the planets would take towards the sun if tangential velocity was reduced to zero?

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**Open Notes Post Lab Return your clickers Normal procedures:**

Cell phones out and on silent Open notes, not open text You will NOT need a calculator When you are done, you can start tonight’s HW: Read and study CH 12 Complete # 21-24, 26 1 point each, and 1 point for random problem graded on correctness = 6 points total Finish your COMPUTER LABS! Just because we did the Post Lab does not mean we are DONE with them! You still have a CLOSED NOTES TEST on Ch. 9 & 12 (April 11th), and you could have a CH. 12 open notes quiz at any time!

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Isaac Newton Initial calculations didn’t work

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**Isaac Newton Initial calculations didn’t work**

Placed theory in a drawer for 20 years

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**Isaac Newton Initial calculations didn’t work**

Placed theory in a drawer for 20 years When the comet of 1670 came, Halley convinced him to re- look at it. (the comet’s namesake)

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**Isaac Newton Initial calculations didn’t work**

Placed theory in a drawer for 20 years When the comet of 1670 came, Halley convinced him to re- look at it. (the comet’s namesake) Produced the Law of Universal Gravitation

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**12.4 Newton’s Law of Universal Gravitation**

Newton’s law of universal gravitation states that every object attracts every other object with a force that is directly proportional to the mass of each object, and inversely proportional to the distance squared Newton deduced that the force decreases as the square of the distance between the centers of mass of the objects increases.

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**12.4 Newton’s Law of Universal Gravitation**

The force of gravity between objects depends on the distance between their centers of mass.

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Gravitational Force The force is extremely small and for most tangible things it is too sensitive to measure Attraction of person to another person is hardly measurable….but the attraction of person to the earth is what we call weight

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**Is this a new diet infomercial???**

12.4 Newton’s Law of Universal Gravitation Your weight is less at the top of a mountain because you are farther from the center of Earth. Is this a new diet infomercial???

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**12.5 Gravity and Distance: The Inverse-Square Law**

Main Concept #5 Gravity decreases according to the inverse-square law. The force of gravity weakens as the square of distance.

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**12.5 Gravity and Distance: The Inverse-Square Law**

This law applies to the weakening of gravity with distance. Gravity weakens by the INVERSE SQUARE of the distance. For example, if we were to make earth 9 times as far from the sun…. The square of 9 is 81. The inverse square of 9 is 1/81 Therefore, if Earth was 9 times as far from the sun, then gravity would be 1/81 as much.

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Inverse Square Law

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**How does the force of gravity change with distance?**

12.5 Gravity and Distance: The Inverse-Square Law How does the force of gravity change with distance?

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**12.4 Newton’s Law of Universal Gravitation**

The Universal Gravitational Constant, G The law of universal gravitation can be expressed as an exact equation when a proportionality constant is introduced. The universal gravitational constant, G, in the equation for universal gravitation describes the strength of gravity… the only problem was, people couldn’t figure out the value of G!

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**12.4 Newton’s Law of Universal Gravitation**

Measuring G G was first measured 150 years after Newton’s discovery of universal gravitation by an English physicist, Henry Cavendish. Cavendish accomplished this by measuring the tiny force between lead masses with an extremely sensitive torsion balance.

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**12.4 Newton’s Law of Universal Gravitation Measuring G**

G was first measured 150 years after Newton’s discovery of universal gravitation by an English physicist, Henry Cavendish. Cavendish accomplished this by measuring the tiny force between lead masses with an extremely sensitive torsion balance.

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**12.4 Newton’s Law of Universal Gravitation**

Measuring G A simpler method was developed by Phillip Von Jolly Mercury Flask and a 6 ton lead ball Measured the shifts in the Force readings when he rolled the massive lead ball under the set up Used that to determine G

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**12.4 Newton’s Law of Universal Gravitation**

Cavendish’s first measure of G was called the “Weighing the Earth” experiment. When G was first measured in the 1700s, newspapers everywhere announced the discovery as one that measured the mass of Earth. (because that was the missing variable in the equation!) Once “G” was known, the mass of Earth was easily calculated.

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**Try to calculate G! View at least 2 rows of data from your activity**

You have m1, m2, and the distance… You also have the force of gravity Plug in solve for G WRITE DOWN YOUR WORK ON LOOSE LEAF!!! Solve for G for at least 2 rows!

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**The value of G tells us that gravity is a very weak force. **

12.4 Newton’s Law of Universal Gravitation The value of G tells us that gravity is a very weak force. It is the weakest of the presently known four fundamental forces. The 4 forces are: Gravity Electromagnetic Nuclear (weak) Nuclear (strong) We sense gravitation only when BIG masses like that of Earth are involved.

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**12.4 Newton’s Law of Universal Gravitation**

What did Newton discover about gravity?

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**We are now going to try the math…**

Take a worksheet READ the front Think about the SOLVED PROBLEMS on the front Try the rest of the problems on the front and back. NOT SURE? CHECK IN W/TEACHER! 6. When you are done, review the HW #8-12 with your peers. 7. After practicing the math, you should very easily be able to check and correct this HW. 8. NOT SURE? CHECK IN W/TEACHER!

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1 = 1 . 1 1 2 ??? = 2 . 2 1 2 ??? = 4 1 2 4 = 4 1… gravity is 4x stronger!!! (or 4x as strong, 4x more, etc) ??? = 4 1

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1 = 1 . 1 1 2 ??? = 1 . 1 (½ ) 2 ??? = _1_ (½) (½) 4 = _1_ (1/4) gravity is 4x stronger!!! (or 4x as strong, 4x more, etc) ??? = _1_ (1/4)

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**We are now going to try the math…**

Take a worksheet READ the front Think about the SOLVED PROBLEMS on the front Try the rest of the problems on the front and back. NOT SURE? CHECK IN W/TEACHER! 6. When you are done, review the HW #8-12 with your peers. 7. After practicing the math, you should very easily be able to check and correct this HW. 8. NOT SURE? CHECK IN W/TEACHER!

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Universal Gravitation

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