13 Universal Gravitation March 21 st /24 th HW due – prep for quest HW assigned: Read & Study 12.1-12.3; complete #1-7 at end of chapter In class today:

13 Universal Gravitation

March 21st/24th

• HW due – prep for quest • HW assigned: Read & Study 12.1-12.3; complete #1-7 at end

of chapter • In class today:

– DO NOW: Time to prep for quest– Reviewed rest of Ch. 9 HW– Took Quest– Ch 12 - Which of the 4 fundamental forces is the strongest?

• DEBATE:– Students will choose Electromagnetic, gravity, strong nuclear, or weak nuclear –

choose a side of the room; can move at any time based on arguments and rebuttals

• DEBATE:– If gravity is so weak, why do we notice gravity between us and Earth?– Why do we notice gravity between us and Earth, but not us and other stuff in this

room?

– Pending time, Started Ch. 12, universal gravitation 12.1-12.3 slides


Take out your HW!

• #8 – 12

• #13 – 15– (both at the end of CH 9)

• Rapid Popcorn review – PAY ATTENTION

• You will have another 5 minutes after this to prep for your Open Notes Quest


Quest

• Normal procedures apply – phones / mp3s out and silent on your desk

• May use notes and a calculator

• When you are done, you can try the extra credit… STAPLE TO YOUR QUEST and turn both in TOGETHER!!!

• When you are done, you may start tonight’s HW, or next class’ HW


Gravity…• Is difficult to measure in everyday life• Is something we take for granted• Is the one of the 4 fundamental forces :

• gravity, • electro-magnetism, • strong nuclear forces (which hold the nucleus

together)• weak nuclear forces (involved with radioactive

decay weak nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)


DEBATE!• Which of the 4 fundamental forces is the

STRONGEST? (think, pair/share, then debate!)• gravity, • electro-magnetism, • strong nuclear forces (which hold the nucleus

together)• weak nuclear forces (involved with radioactive

decay weak nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)


DEBATE!• Move to your assigned part of the room and discuss. I

will be calling on people at random to defend their choice. If at any time you want to switch sides, feel free• FRONT RIGHT: gravity• FRONT LEFT: electro-magnetism • BACK, CENTER: strong nuclear forces (which hold

the nucleus together)• BACK, CENTER: weak nuclear forces (involved with

radioactive decay weak nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)


DEBATE!• FRONT RIGHT: gravity• FRONT LEFT: electro-magnetism • BACK, CENTER: strong nuclear forces (which hold the nucleus together)

• BACK, CENTER: weak nuclear forces (involved with radioactive decay weak

nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)

• It takes the mass of the ENTIRE WORLD to keep this ONE PAPER CLIP on my desk…which I can easily overcome with ELECTROMAGNETICS!

• It takes the mass of the ENTIRE WORLD to keep this SHREDDED PAPER on my desk…which I can easily overcome with ELECTROMAGNETICS!

• If nuclear forces were weaker than gravity, then you wouldn’t have a chair to sit on…matter of fact, you wouldn’t exist! Gravity would literally RIP APART EVERYTHING!


DEBATE!1. strong nuclear forces (which hold the nucleus together)

2. electro-magnetism

3. weak nuclear forces (involved with radioactive decay weak nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)

4. gravity• It takes the mass of the ENTIRE WORLD to keep this ONE PAPER CLIP

on my desk…which I can easily overcome with ELECTROMAGNETICS!• It takes the mass of the ENTIRE WORLD to keep this SHREDDED

PAPER on my desk…which I can easily overcome with ELECTROMAGNETICS!

• If nuclear forces were weaker than gravity, then you wouldn’t have a chair to sit on…matter of fact, you wouldn’t exist! Gravity would literally RIP APART EVERYTHING!


DEBATE!1. strong nuclear forces (which hold the nucleus together)

2. electro-magnetism

3. weak nuclear forces (involved with radioactive decay weak nuclear forces: are involved with carbon dating, are a source of radioactivity, etc..)

4. Gravity

• If gravity is SO WEAK… then WHY do we notice it acting on us, everyday? Discuss in your groups – I will randomly select point people to defend

• If gravity is exerted by EVERYTHING in the universe with MASS… then WHY do we notice the gravity earth exerts on us, but not the gravity we exert on all the other stuff in this room?


Everything pulls on everything else.


Gravity was not discovered by Isaac Newton.

What Newton discovered, (legend holds it was prompted by a falling apple), was that gravity is a universal force—that it is not unique to Earth, as others of his time assumed.


MAIN CONCEPT #1Newton reasoned that the moon is falling toward Earth for the same reason an apple falls from a tree—they are both pulled by Earth’s gravity.

12.1 The Falling Apple


Newton understood the concept of inertia developed earlier by Galileo.

• He knew that without an outside force, moving objects continue to move at constant speed in a straight line.

• He knew that if an object undergoes a change in speed or direction, then a force is responsible.



According to legend, Newton confirmed his thoughts about gravity while sitting under an apple tree.



Newton saw the apple fall, or maybe even felt it fall on his head. Perhaps he looked up through the apple tree branches and noticed the moon.

• He may have been puzzled by the fact that the moon does not follow a straight-line path, but instead circles about Earth.

• He knew that circular motion is accelerated motion, which requires a force.

• Newton had the insight to see that the moon is falling toward Earth, just as the apple is.



MAIN CONCEPT #2The moon is actually falling toward Earth but has great enough tangential velocity to avoid hitting Earth.

12.2 The Falling Moon


• Newton realized that if the moon did not fall, it would move off in a straight line and leave its orbit.

• His idea was that the moon must be falling around Earth.

• Thus the moon falls in the sense that it falls beneath the straight line it would follow if no force acted on it.

• He hypothesized that the moon was simply a projectile circling Earth under the attraction of gravity.



If the moon did not fall, it would follow a straight-line path.



• If a cannonball were fired with a small horizontal speed, it would follow a parabolic path and soon hit Earth below.

• Fired faster, its path would be less curved and it would hit Earth farther away.

• If the cannonball were fired fast enough, its path would become a circle and the cannonball would circle indefinitely.

Newton compared motion of the moon to a cannonball fired from the top of a high mountain.

His Original Drawing!


Both the orbiting cannonball and the moon have a component of velocity parallel to Earth’s surface.

This sideways or tangential velocity is sufficient to ensure nearly circular motion around Earth rather than into it.

With no resistance to reduce its speed, the moon will continue “falling” around and around Earth indefinitely.



Tangential velocity is the “sideways” velocity—the component of velocity perpendicular to the pull of gravity.



If the force that pulls apples off trees also pulls the moon into orbit, the circle of the moon’s orbit should fall 1.4 mm below a point along the straight line where the moon would otherwise be one second later.



It wasn’t until after Newton invented a new branch of mathematics, calculus, to prove his center-of-gravity hypothesis, that he published the law of universal gravitation.

Newton generalized his moon finding to all objects, and stated that all objects in the universe attract each other.



Why doesn’t the moon hit Earth?



MAIN CONCEPT #3Newton’s theory of gravity confirmed the Copernican theory of the solar system.

THINK BACK - - What is the “Copernican Theory”?

12.3 The Falling Earth


No longer was Earth considered to be the center of the universe.

• It became clear that the planets orbit the sun in the same way that the moon orbits Earth.

• The planets continually “fall” around the sun in closed paths.



The tangential velocity of Earth about the sun allows it to fall around the sun rather than directly into it.



What theory of the solar system did Newton’s theory of gravity confirm?



MAIN CONCEPT #4

Newton discovered that gravity is universal. Everything pulls on everything else in a way that involves only mass and distance.

12.4 Newton’s Law of Universal Gravitation


• HW due – Ch. 12 #1-7 • HW assigned:

– Read & Study 12.4 – 12.5; complete #8-12 at end of chapter – Finish today’s notes if necessary!

• In class today:– We will continue Ch. 12, universal gravitation – Pending last class’ progress, may start/complete the 12.1-12.3

Newton’s Law of Universal Gravitation slides – Remainder of class to complete the web based Universal Gravitation

Lab

• Do Now:– Close Read – directions to be announced!– TAKE BOTH PAPERS on my desk

March 25th/26th


Francis Thompson• Was an English poet and ascetic (abstained from EVERYTHING including

food). (father was a doctor = wealthy)• Went to University and Medical School, but took no real interest in his

studies and never practiced as a doctor, moving instead to London in 1885 to try to become a writer. No luck; had to sell matches and newspapers for a living.

• During this time, he became addicted to opium, and lived on the streets• In 1888 he was 'discovered' after he sent poetry to the magazine Merrie

England. He was sought out by the editors (husband & wife) and rescued from the verge of starvation and self-destruction. The couple gave him a home and arranged for publication of his first book, Poems in 1893.

• Critics loved him, and Tolkien (Lord of the Rings author) was a fan! • But…He remained ill for the rest of his life. (extreme poverty, ill-health, and

an addiction to opium took a heavy toll on Thompson, even though he found success in his last years.)

• He eventually died from tuberculosis, at the age of 48.


DO NOW - Close Reading Steps• While you are

completing these steps, your ultimate goal should be to consider the following question:

• How does this poem relate to Newton’s Law of Universal Gravitation? Cite specific evidence!

13 Universal GravitationAll things

by immortal power

near or far

to each other

hiddenly linked are.

That thou cans't not stir a flower

without troubling a star.

• How does this poem relate to Newton’s Law of Universal Gravitation? Cite specific evidence!



Your Task…

• Discover Newton’s Law of Universal Gravitation!

• Using a PHET simulation, you will explore Newton’s Law of Universal Gravitation. (Newton did this WITHOUT computers….you can definitely do this easily with technology!!!)

• Finish the Simulation Worksheet up to #17 – if not, it is HOMEWORK!

Documents

13 Universal Gravitation March 21 st /24 th HW due – prep for quest HW assigned: Read & Study 12.1-12.3; complete #1-7 at end of chapter In class today: