Kepler's Laws and How Newton Got Cool | Doc Physics

[@JMRpink101]

I cannot express how clear this video is. PERFECT. I was literally smiling like an idiot throughout it because it alleviated so much confusion. Definitely sharing.

[@Shinywhite]

Your explainings are godly

[@edidan4287]

Doc S brings the clarity!! :)

[@debendragurung3033]

This is where I was stuck for quite a while as to how Newton propsed laws of Gravity? I really couldnt see why he would do mulplicative operation on two masses out of any other mathmatical operations. So it was his observations but on Keplers data, that he formulated the idea. NEAT.

[@sammyasher]

yooo literally the exact thing I was just trying to figure out - why multiplication and not addition? looking forward to this video

[@Kukuzcam]

@4:20 looks like an eye, well done video. Thank you

[@xxslamxx]

Great video. I love how you pronounce ''squared'', btw; 10:54-11:02 made my day.

[@DocSchuster]

Yay! Thanks!

[@jameskdoherty009]

Doc Schuster It is a great video, where did you get that pronunciation? Is that how they said it in Newton's time?

[@pipertripp]

@@jameskdoherty009 he's just a playful scamp.

[@h.a.2107]

man, you're awesome, that was a great help.

[@dextoor]

Cool Assessment! Thank you sooo much for doing this!

[@EmperorMato]

What a great presentation. I agree with others commenting that it made things very clear and comprehensible. Regarding Kepler's and Newton's laws I read an interesting idea: Walter W. Bryant wrote about the time Kepler discovered his laws and that "from that moment the idea of universal gravitation was in the air, and hints and guesses were thrown out by many; and in time the law of gravitation would doubtless have been discovered... even if Newton had not lived. But, if Kepler had not lived, who else could have discovered his Laws?" (1920) Great honor to the great astronomer, what do you think?

[@ChristianHildebrandtDK]

7:03 "r2 the 3 halves" sounds somehow like being sung on seven nation army theme!

[@rockyjoe3817]

TRUE XD

[@lenael4747]

I like the way you explained everything in a funny manner. I wish every teacher was like that, saying " I don't know". 😂 LOL.

[@CaptainCalculus]

2:36 "fairly easily"??

[@brendansmith5529]

Great video! However I think there's a couple historical inaccuracies-- Newton didn't introduce the Gravitational Constant (as a universal constant) himself, nor did he have any inkling of the mass of the sun. Basically everyone back then (except Descartes) did math with geometry instead of algebra, so Newton, like Kepler, was only able to say that the force was proportional to mM/r^2. The modern algebraic notation didn't emerge until centuries later.

[@ZHike360]

Squr

[@rasmusfalk-jensen8221]

Thank you so much! This was exactly what I needed for my school project

[@arbadon]

I'm a bit confused.. At 10:30 you define the radius of the orbit. But how can you define the radius of an ellipse as only one distance? The radius is different on the X and Y axis. Is there some kind of calculation needed or do you assume it's a circle here? Thank you!

[@DocSchuster]

ralph houthoofdt I am totally assuming a circle here. Very sloppy. There would probably be a calculation with semi-major and semi-minor axes if we were being careful.

[@dimuthiiddawela8994]

Great video ur so good at teaching

[@kevinmenting7727]

Excellent Derivation man, presented in a understandable and funny way, love it!

[@pbjcyclops9250]

this video is awesome! i understand the first and second laws great now! you did an amazing job with the third, and i understand it a ton better now, but its really complicated lol

[@lrp1126]

Holy shit. I actually get it now! You're amazing!

[@DocSchuster]

Thank, Lauren!

[@rpicorelly]

THank you! You actually made learning fun!

[@Stan-san]

very cool and spontaneous!

[@Hahduyban]

Great vid. Great explanation.

[@JanixCherie]

daayum thanks man this helped a lot actually haha :D loved the way you explained this.

[@brookestephen]

you said r is the radius of the sun... it's the radius of the planet's orbit.

[@alknowledge183]

I referred to a textbook, it states semi-major axis, a can replace radius, r in Kepler Third Law for a elliptical orbit. However, why uses semi-major axis but not semi-minor axis?

[@leahg180]

That proof of Kepler's third law was really neat, although I am now curious about a proof without generalizing the ellipse to a circle... maybe polar coordinates would do the job here? Also, have you proved Kepler's second law of this channel?

[@DocSchuster]

No, I sure haven't proven the second law, but I'm sure it's somewhere out there.

[@leavethebasket7435]

leahg180 polar coordinates. r=p/1-ecosa where a is angle, e is epsilon the eccentricity cooeficient, and p is L^2/au where a is alpha, which is GmM and u is mu which is reduced mass which is Mm/M+m

[@joebender3662]

How does this change using general relativity because in general relativity the curve isn't a perfect ellipse ?

[@TanerNilluhktaf]

Oh, dang! And Newton was in. - Such a nice story telling! ^ ^

[@Tech_Gamers]

I really want that thread-compass of yours....

[@muhammadisraa6856]

this video is really helpfull.I think you should do more videos about stuff like this for example like orbital mechanics or central forces

[@Ian_Durr]

However Newton didn't figure out Big G! It was Cavendish 110 years later. "Newton didn't even mention a constant sich as G" quoted from by Physics book.

[@williamaderera3371]

hey ,i have a question why sun is at one focus why it does not move to the other one......pls answer

[@nickmanning3555]

You did not take the square root of the constants at the very end. The "some stuff" in the equation at the top should be 2pi/sqrt(Gm). This might confuse some people watching this video and learning these laws for the first tme

[@the_dane9580]

up with you!

[@matrixate]

Actually, in the last step what you put into the "stuff" would be the square root of that, not what you actually derived; unless you square both sides of the top equation. Regardless, brilliant presentation.

[@fiddlershopgoogle7623]

Your question about the sound made in "Fast Five" disappeared but in case you didn't figure it out, just play Ponticello (very close to, almost on, the bridge, without too much pressure) while doing a glissando. The sound they get on "Fast Five" of course is more effective with a large string section. :)

[@fiddlershopgoogle7623]

This is Pierre BTW (Fiddlerman) didn't realize that I was logged in as Fiddlershop (Micheal)

[@RougeSamurai77]

?????????????

[@svenvalbruak5197]

Lol they plugged it into their ti-89s. This was such an epic video

[@pencilmein6646]

I came here to figure out what a semi major axis is from my high school introductory astronomy lesson and this is what I see...it's-it's beautiful ;v;!!

[@THEPRINCESSAMAZING]

That was awesome!

[@Gabcikovo]

1:01 excuse me?! This is NOT an ellipse, this is a circle!

[@physicsconceptsbytusharkha7638]

One doubt. While calculating the time period you assumed a circular motion of planet. And not elliptical. And what r should we take for elliptical orbit.

[@FugieGamers]

you proved keplers third law for circular, not eliptical motion.

[@ZeroGunzRoyCHP]

I have a question: For centripetal force, you wrote Fc, for centripetal acceleration, you wrote acp, so is it c or cp???

[@DocSchuster]

Zero Gunz Certainly not consistent! Sorry. Choose what you like. I'm a big fan of F_c and a_c typically.

[@alphalunamare]

laughed my socks off at the 'slowing down' epiphany.

[@vivalibertasergovivitelibe4111]

That is a really great video. Just a little question: in the last equation it says r^3 and in kepler's it says r^3/2. is there something I have missed?

[@DocSchuster]

+Janniboy “abcnon” lp Look at the power of T.

[@vivalibertasergovivitelibe4111]

+Doc Schuster oh thanks

[@DavidAsta]

Excellent video. Just a comment on what you say at 1:00: "foci" is the plural for "focus", so it's wrong to say "these are the 2 foci of the ellipse". Correct would be to say "these are the foci of the ellipse" or "these are the 2 focus of the ellipse". Cheers.

[@DocSchuster]

Thanks! But when you go shopping, do you come home with nine carrot?

[@hiddensheepy8736]

David Asta I think the second suggestion of your response at the end should be in plural form, rather than in singular. As the person who posted the video commented, would you come home [and say that you had] with [you] nine carrot, or nine carrots? Cheers.

[@armuttaqien6092]

Hi, I'm a novice in physics, I'm wondering according to the illustration of Kepler's law. how could elliptical shape can be adapted into circle were used by Newton to deriving gravitational law, the centripetal, or variable of circumference 'r' = radius of orbit circle while we know the orbit of the planet itself in ellipse form? thanks

[@Rebius]

+Ar Muttaqien If you take the focal points of the ellipse, and bring them closer together, the shape of the ellipse will start to look more like a circle and if you got those two focal points over another, than you get a circle. Because orbitals of Planets in our solar system are ellipses with very small distance between those two focal points, it is almost a circle and therefor it is easier to calculate as if it was a circle. Physicists like to approximate things to an ideal, because even though it is not 100 percent correct it describes it quite well.

[@jimkeller3868]

Confused. If I take the square of the period of say Venus, it equals the radius cubed. If I place the constant you've derived into that relationship, does the constant cancel itself out? Why is it necessary? I follow how you've derived it, but have no idea about its relevance. For example, I have read this regarding this constant: "But, if we express in Astronomical Units and in Earth years, then it (the constant presume) actually comes out to be 1! How is that possible?

[@DocSchuster]

Jim Keller Theoretical physicists love their unit transformations. They are correct that 1 = 1^(3/2). The constant is not intrinsically valuable to anyone except folks who are looking for planets around other stars or trying to find dark matter.

[@jimkeller3868]

Doc Schuster But how do the units of mass and "G" function in that constant. For example in Newton's law of gravitation, the units of kg and meters cancel leaving only Newtons as the expression of force. I still don't understand where "m" and "G" go in Newton's constant that you have described. If I plug in numbers for G and M I get huge numbers not related to "T" or "a" Am I to view "M" as "1", meaning one solar mass, and not the actual mass of the sun in kg? That would help, but then how is "G" to be taken?

[@DocSchuster]

Jim Keller Equations are still valid upon unit transformation, but you must transform all the variables into a self-consistent system of units. I sure don't know of one with AU and Earth years, as those are both heuretic. People who transform into those units either have no idea what they're doing OR they are theoretical physicists who are comfortable with units not working out. I personally have hesitations working in systems where the units are not consistent, but some of my friends can handle it. I am not an expert in weird unit systems. Maybe Dr. Physics A (also on youtube) can help. I don't remember what his research was...

[@muhammadisraa6856]

Btw,can you explain is there any special characteristics for the suns gravitational field that causing all the planets that orbitting it to have constant angular momentum so that the seconds law (dA/dt= constant) is obeyed??

[@ayushsati918]

At what place it will be absolute fastest and absolute slowest and why?

[@mohab1029]

lol i know this is 2 months old but it will be faster when the planet is closer to the sun and slower when it is far away because as the planet moves away from the sun the gravity decreases (becomes weaker)

[@zegerrijs5942]

Can you prove Kepler's 3rd law in the more general elliptical case? You have convinced me it is true for circular orbits, but what about elliptic ones?

[@DocSchuster]

Right...soooo...I guess it won't help if I point out that Kepler never proved it in ANY cases, eh? I don't know that I've ever seen a general proof, though. Maybe I'll assign that as homework!

[@yobabyyo]

I like it!

[@vernerspindler734]

A thinner pen might make it look less messy!

[@MoustafaMezher]

how they did know what is the mass of the sun?

[@emilycorneliussen]

why do i get 470 days when i try to use this method to calculate T for earth? Does anyone have a fast answer?

[@DocSchuster]

Bitte schön!

[@feynstein1004]

Sind Sie Deutsch?

[@RougeSamurai77]

Wow I wish I was as cool as newton.

[@SimchaWaldman]

He thought about the 2nd law first. Then discovered the 1st law.

[@multiakc9232]

ok its goood bro

[@GatorAidMedical]

why does he say squrr it's really annoying!!

[@bestredditstories1158]

Harsh Jha The question on everyone's mind.

[@norauniverseindia3161]

Just bare with it

[@marcrogue5268]

People keep making enfaces on elliptical vs circular. A circle is but a special case of an ellipse

[@esperanzazendejas8451]

squrr lol. kool video ! thank you

[@Ericapires12]

cool teacher ever lol

[@whitewolf1298]

The only problem with this is that Newton's gravitational forces are absolutely dependent on the planets describing perfect circles around the sun. The only other problem with this is that the apparent motions of the planets are being heavily influenced by... absolutely nothing. So if we just toss out the law of causality everything in Kepler's universe is just peachy. Meanwhile, I think those flat eathers have a point...

[@jimmyalderson1639]

Can you not pronounce 'squared'? It's a minor nit pic and i actually quite like the way you say it, it's just strange

[@christopherellis2663]

Faux sigh? 😊 How would you say focaccia? Veni, vidi, vici? But you have not demonstrated the maths.

[@prateekgurjar1651]

Uranus

[@TrickysBen]

Shout out to 3rd hour yooooooooooooooooooo

[@mo-daniel-369]

"street cred" lol

[@Gabcikovo]

You draw an ellipse differently. My Dad taught me to draw an ellipse with 2 pins when I was around 9 years old! I can't believe you did this video and people actually comment on it praising your bullshaite. Oh man!

[@Gabcikovo]

This is how you draw an ellipse with 2 pins: kzbin.info/www/bejne/injTdJ6pf9OMmqM

[@Gabcikovo]

Kepler's laws explained with an actual ellipse, not a circle 😄 kzbin.info/www/bejne/eqfSlmt_l5p3Z9E

[@Gabcikovo]

And now we all have a good laugh, doc Schuster or what's your name 🤭😄😉🍕

[@jonathanali9527]

Squrr

[@gabriellasut5980]

m times v squirrel over r

[@daffavirwandy7694]

Cringe. But hilarious :)

[@adamluyt8350]

Squrr