Introduction to Gravity

[beer94]

you're an artist too?

[Kricardose]

I am very happy to see the vidoe Basics of gravity and the Law of Universal Gravitation after you give this

[bebeheuy]

I Love The Video Basics of gravity and the Law of Universal Gravitation It Can Increase My Knowledge

[Mjhond]

Steady I Really Like This Video Basics of gravity and the Law of Universal Gravitation

[kroese1870]

Grand Unified Theory by Nassim Haramein, watch that before enter into TOO MUCH classical physics.

[moopy239]

Love Khan's videos. He called Newton "one of top 5 minds in human history" True, with respect to science, but minds work in different ways...How about Beethoven, Bach, Alexander the Great?

[MultiApodyopsis]

@moopy239 How about the top 5 minds that helped the human kind develope more knowledge? Because they are the important people not singers or sports players! The smart people will help the world not idiots that play football or whatever.

[MultiApodyopsis]

@moopy239 how has poetry and wars helped our world?

[bladervinay]

Brilliant video made me think a lot on gravity

[faultbreak]

You are an incredible artist. Pretty good stuff. Do you draw or paint at all? I'd like ot see something you have done.

[themariogamer99]

Thank you so much Sal!!!

Just thought of something... How do we find the time after which to objects in free space will collide due to each others gravity? given F = G*m1*m2/d^2 we can find the objects' (initial) accelerations using a = F/m.... But as the distance between them decreases won't the force between them ( and thus accelerations) also increase? Is it possible to model this using a differential equation? If so can it be solved? Can someone pls help me out on this? Thanks!

[purplehaze216]

that was a good computer

[Ciwan2]

This was freakin' awesome. Thank You SAAAAALLLL.

[pelasot1]

Thank you so much for this playlist. No. 1 reason why I have a 100 in physics. Otherwise I'd be barley passing!

[cherryboyv]

mechanics makes so much sense now after watching this video :)

[kbdalcour18]

Ow my computer screen just flew into my face ):

[NineLivesProductions]

hahah I put my hand up to my screen at 6:50

[JpJangz]

hi, i have 2 question sorry ><

First, so is the G 6.67 x 10 to the power of negative 11 is the universe G? and that all gravity is affected by the mass and the radius of the star or planet itself?

Second, so lets imagine another planet with mass greater than earth but however smaller in diameter analogous to a small 10kg metal ball(X planet) with a humongous 1kg paper ball(earth) were to come near earth, then will earth accelerate towards it? Since it is also affected by radius..Sry~

[shjh69fgx]

please man I want to to get a calculator like urs

how can I download it ?????

[latetilla0205]

''a pretty fascinating dude'' hahaha this guy cracks me up!! Thank you for your vids!

[menarelikepeople]

i like your smiley face :)



[Podcan]

Love the way you teach! What software are you using to scroll and notate on?

[terios01234]

you physics interesting



[hanansleman]

he asked "why" and in my turn i ask him "why"..."why did you even bother !!! students were happy before that question" :D

i like the theory that says "the apple hit him on the head" and wish it was a watermelon instead ...so that he will keep his "why" to himself :P

[ginabirthday]

i loooove love love your lecture !lenable me to study in the U.S.YA!!

[MRJerrod410]

Sal, you wrote that force (F) was a vector but you did not put the radial unit vector (r) on the other side of the equation.

[klaramigbra]

i'm going to watch a khan-video a day during the summer to prep for school, thanks Sal! But whar does accelaration (a) mean?

[Auautonic]

LOVE YOUR DRAWING!!

[petercourt]

Why aren't you falling 9.8 m/s^2 towards the Earth when you're standing up normally? What forces change when you jump off a building to cause your acceleration to increase?

[vicksoma]

@petercourt Gravity is still working when we're standing up normally, but of course when we're on the ground we can't go through it, so we don't move (but the force is still acting on us). The force that keeps us from going straight through the earth all the way to the center is the electromagnetic force from the electrons in your body and in the ground, they repel each other. The electromagnetic force is WAY stronger than gravity, so we don't fall through the ground.

[heavymetaldeath4life]

@vicksoma Strange. I always assumed that according to Newton's 3rd law of motion, every action has an equal and opposite reaction thus the surface of the earth pushes us back.

[vicksoma]

@heavymetaldeath4life There is a force called the Normal Force that counteracts other forces. So in the case of gravity, our bodies are pulled down, but the normal force reacts and pushes back with an equal and opposite force, leaving us staying still. The normal force comes from the electron interactions between us and the floor, by the way. I'm not exactly sure whether this counts as Newtons 3rd Law because i don't know if gravity is really an "action"

[camelCaseFTW]

u have awesome drawing skills lol

[skillphiliac]

A pretty fascinating dude.

[warvad]

I am seconding the comment suggesting a video on special and general relativity.

[mauroprovatos]

What playlist are the new gravity videos in?

[nakedapedude]

Gravity is just a theory! Magical falling should also be taught in schools!

[BlackBeardDelight187]

Everytime I watch videos on gravity I feel heavy

[ch00bz0rzzz]

I have a question. If I’m pulling the earth towards me with 500N of force and the earth is pulling on me with 500N of force, then wouldn’t something somewhere add up to 1000N?

[kevkool230]

@ch00bz0rzzz no. Force are vectors so directions matter. The two forces point opposite directions so they cancel

[beforever]

What about the other four minds of human history, I'd like to know Sal'!?

[MoGaDeX]

I have a question: where did he come up with that equation?

[BlackBeardDelight187]

@MoGaDeX Some of his ideas came from these dudes: Copernicus, Brahe, Galileo & Kepler.

Believe me or not, these ideas can be traced through the Renaissance down to the Library of Alexandria and beyond

[noxure]

I'm afraid you got some details wrong.

Newton's breakthrough was envisioning that the orbit of the moon and the apple falling on the ground being the result of the same force.

The scientists before Newton weren't idiots, they already knew a lot about how gravity. Newton was the one who developed the calculus to describe it precisely.

Also, Newton was only concerned with "how", because he was very pious he never asked himself "why". He simply believed God made it that way, period.

[smartpartzzkidd]

do quantum field theory

[Elsoddo]

"The falling apple" is a misconseption. What gave him the idea was observing a heavenly object curve around the sun. Niel DeGrasse Tyson explains it better.

[orochimarujes]

I got introduced to gravity a long time ago.

And it hurt!

[shaheerftw]

@orochimarujes lol nice



[AdmiralJef]

Imagine if you tied a rope to an airplane and pulled on it while wearing roller skates. The tension on that rope is like the gravity between you and the Earth. You are pulling on the plane but there is the exact same amount of force pulling on you as well. That force is enough to move you forward, but since it is so massive, that same force on the plane has no noticeable effect.

[kcolber]

Don't you think you should talk about Robert Hooke? Newton was a douche-bag.....

[Swetlana0]

This is super duper duper duper duper DUPER awesome!

[projecthomecoming]

Actually.. I've been introduced to gravity a few times before....

[MarvelsofaLifetime]

This was good and all, but Gravity is just a theory, and it doesn’t fit my biblical worldview. I’d rather think that God’s magical hands are what’s responsible for masses staying attracted to each other.

[floopsie666]

@MarvelsofaLifetime Haha nice one...made me laugh.

[dannes22]

@MarvelsofaLifetime well you're an idiot.

btw, it's not a theory.

herp derp

[MarvelsofaLifetime]

@dannes22 Lol I don’t know what’s more ridiculous, my comment, or the fact that you couldn’t realize I was joking and being facetious.

[dannes22]

@MarvelsofaLifetime Well, Have you noticed the amount of idiots on the internet?

there is quite a lot of them, quite a lot.

See dussins of idiots with those kinda comments, who are serious.

[Dryltd]

I am so strong. I pull the earth toward in my sleep

[sodaxcandy08]

freakin newton!!!!!

[TreachMarkets]

When I saw the video's title I thought maybe it was one of those skateboarder crash videos.

[pommyrooter]

The question "why?" is the most powerful ever asked.

[Omnilegence]

@pommyrooter Why?

[pommyrooter]

@Omnilegence, Very nice.

[Inkognitohaloramics]

I watch these videos for fun.

[torstein99]

Oh shit..

I just got my computer on my face!

[luiscosta1992]

where do you get the seconds from?

[jsnprofessor]

fascinating DUDE!!!!!!!!!!

[VincentTheBoss]

Can somebody explain to me why the earth doesn't fly into the sun?

[Anubispop2]

@VincentTheBoss because the earth has angular momentum. the earth gets pulled towards the sun, it just keeps missing, because the direction of the gravitational force constantly changes. without angular momentum, the earth would fly directly into the sun.

[LoopuleasaIonut]

@VincentTheBoss The earth is constantly falling into the sun. Also, the earth is on a trajectory around the sun. Like a cannonball is falling around earth when it is launched at a standard speed and lands afterwards, if you launch the cannonball very, very fast, it's trajectory would follow the curvature of the Earth ( thus following the "roundness" of the Earth ).

Try searching for "Neil deGrasse Tyson orbits" on ytube. I know a video of him explaining it very well.

[VincentTheBoss]

@LoopuleasaIonut Aha I understand now, I had heard the canonball example before, but isn't it true that eventually the ball would fall down because of friction? So if if everything lasts long enough eventually the earth will fly into the sun, or is the impact of the gases and particles in space so minimal that it can absoluteley never happen?

[floopsie666]

@VincentTheBoss There is no friction in space; space is a vacuum.

[VincentTheBoss]

@floopsie666 No it isn't. Compared to the atmoshere it is, but there are a lot of particles in space, espacially within a solar system. Even in intergalactic space there are still a few particles per square meter.

[floopsie666]

@VincentTheBoss There is no friction in space lol.

[LoopuleasaIonut]

@VincentTheBoss It is minimal compared to the huge masses involved ( also think about this: when the sun heats Earth it is propelled outward a tiny bit ) Friction and space are not good friends. A lot of forever alone particles in space. Furthermore, the particles and radiation in space come from all directions so on direction won't be favored over another. Not even a meteor impact will change Earth's orbit very much.

[schlynn]

Isaac Newton was a douche. Gottfried Leibniz was a much much better mathematician. Why do you think we use Leibniz notations for derivatives (d/dx) and not newtons. Newton also said he was glad that Leibniz died.

[CRISNCHIPS12398]

@schlynn He was obviously not a very nice person. But there is no denying that he was one of the greatest minds in human history.

[schlynn]

@CRISNCHIPS12398 When I think of great minds I think of a massive list before I get to Newton. Srinivasa Ramanujan, Descartes, Riemann, Euler, Pythagoras, Fourier, the list goes on and on.

[GelzBelz]

1 person never got hit in the head with an apple

[GelzBelz]

even through summer time, i watch khan... i love it

[HabeKeinMitleid]

@GelzBelz Can't get enough!! I know what you mean. :)

[Swetlana0]

@GelzBelz He is awesome like that.

[Ziibra93]

who paused the video and googled 'The mass of earth' just to see if it really was interesting? I know that I did :P

[VincentTheBoss]

@Anubispop2 Thanks, but why does the direction changes all the time? Because the earth circles thesun?

[LoopuleasaIonut]

@VincentTheBoss It changes all the time because the earth's position changes all the time ( it is moving throught space )

[Rokker815]

shouldn't G and g be vector quantities?

[Rokker815]

@Anubispop2 I thought that you could incorporate g and G into that unit vector, ie (0,0-G) and (0,0,-g) respectively

[RTRVII]

@Rokker815 G is the graviational constant so no. g, yes because it is an acceleration thus a three-vector.

[RTRVII]

@Rokker815 sorry forget my answer ;)

[127miles]

WhY couldn't you made IPS vids before exams! You would have saved my life! Now I'm goingnto het an average grade

[Catatonyx]

Sal, you have the most perfect timing. We're using the gravity laws and Newtons in Extension Science at the moment, and I previously didn't really understand how Newtons work. Now I do. You're a legend!

[Anubispop2]

Sal! In your equation F = G m1m2/r^2 you need to include a vector (\vec r / |r| )on the right side (which has a length of 1)! I know that you already knew that, but maybe you should clarifiy it... Otherwise there is a vector on the left side but a scalar on the right side of the equation. Otherwise the video is great, as always!!

[Vaylemn]

We know why, but we still don't know where, as in where gravity comes from. The hyperspace theory, I think, says that it comes from higher dimensions or another universe.

[Poleschs]

@Vaylemn Einstein said that gravity was the shape of the space itself. Quantum Theory say that gravity is quantized by gravitons. Individual gravitons has not been detected, because they are extremely weak, but gravitons have more or less been proven.

[r4rasa]

32.2 feet per second, per second is the speed in which the earth pulls you when you fall off the building! Thanks Khan

[ASeventhSign]

Isaac Newton, my favorite Jesus fReAk.

[V3rtyX]

i hope you will do a video on special and general relativity

[mikeroweRules12]

@V3rtyX that would make my day i love to see Sal do videos on those two very important topics

[mikeroweRules12]

@V3rtyX that be interesting

[kloneo]

@V3rtyX especially general rel

[swankrecords]

the 5th dimension sent a shockwave to the mind

[paesanng]

Newton didn't know HOW gravity worked. CERN is still looking for the particle mediator called the Graviton, or maybe they gave up.

[shinomora]

Who needs school when you have khanacademy!!!!

[deezynar]

Newton was very sharp but he made a mistake on one of his gravity equations. A Dutch guy ran some experiments and found it and a French woman then fixed the equation.

Just saying.

[HxenGx]

I LOVE NEWTON AND I LOVE SAL!! (:

[aijesse]

Need a video on how gravity works, what is the mechanism of attraction?

[deezynar]

@aijesse

There isn't a mechanism of attraction, space time is warped by matter. Now ask me what that means, I don't have a clue. : )

[paesanng]

@aijesse CERN is still looking for the Graviton, they think that is how gravity works. It's been years and they havent found it. The formula F=(Gmm)/r^2 just shows what gravity does, and now how it works

[danc3hallkrashr]

im so glad you were on colbert so i could know about these videos.

[chocobofarmer2021]

The inverse square law means the 'conserved quantity' radiated from a sphere spreads outward proportional to the square of the radius. That 2 in the exponent of radius always confused me.

[SpoiledLogic]

cool we can download your videos!

[7crazy4u]

SAL you rocks !!!

[chocobofarmer2021]

How did Newton calculate the gravitational constant?

[m8tate]

@chocobofarmer2021

I suppose by knowing the force of gravity on a given object, the mass of that object, the radius of the earth, and somehow knowing the mass of the earth then solving with the law of universal gravitation.

[pqxh]

@chocobofarmer2021 Newton never measured G accurately. It was first done in the Cavendish experiment not long after his death.

[SonofDust777]

Newton was a creationists! That' pseudo-scientist!

[Emanresu56]

@SonofDust777 Yes, Newton was a Creationist. So what?

[Deioproductions]

GRAVITY IS JUST A THEORY, STUPID GRAVITATIONALISTS

[Ariccio123]

@6:35 that's actually a pretty nice sketch of a computer.

[FOOLYCOOLY]

Can't wait till there are more of these. I sort of wish that I knew more about how the units worked-- where seconds squared came from and how G's units interacted with m1m2/r2 to get the units that it does. Google time.

[spinynorman1982]

Carl Sagan said Astrology was bogus. He mentioned that Mars had far less of an impact on our life (in terms of gravity) than the person who delivered you at birth. Because even though Mars is much more massive, it it also much further away than the person. Now we are given the equations to prove it. That THAT pseudo-science!

[wasdom01]

These introductory videos always blow my mind. The force of embarrassment about my ignorance is countered by an equal and opposite force of excitement at gaining new knowledge, leaving me feeling....stretched.

[IslandAtheist]

Gravity Huggers!

[MrChin000]

Hey Sal at 14:24 where you are determining the acceleration from the F= m x a equation you used 68 kg as your mass instead of 70 kg => the acceleration would then be 10.1 m/s^2

[Sephrone]

@MrChin000 He lost weight and was really high above Earth's surface for that measurement :)

[Sephrone]

@Sephrone my mistake, the Earth shrunk :/

[Psam091]

weight is the normal force between the person and the scale. Physics 1!!! lol

[Ferrus91]

Oh and I'm still hoping we eventually get to the divergence theorem and stoke's theorem in the calculus playlist

[Ferrus91]

A good way to show gravitation on a very small scale is using torsion balances. One can 'see' the gravitation effect of a mountain for example.

[gamemaster014]

Wow, i'm attracted to my computer. Awesome!

[RoyceRK]

We know Issac Newton is in Salman's "Top Five Minds of all of Human History", and it's also safe to assume Albert Einstein is also included in this list.

I'm curious as to the remaining three :)

[totojaaat]

@RoyceRK I', guessing Galileo is in that list

[smoothbanana]

The pulling forces being equal took a while for me to click. I just assumed that the pulling force exerted on an object is proportional to its acceleration, i.e. Earth exhibits a higher pulling force on me and so I am pulled towards it. Cheers Sal

[unpenseurquipense]

I love what you're doing Sal. Thank you.

[quitchiboo]

earths acceleration towards Sal is roughly 7*10^-27 m/s^2 , which is immeasurably small

[atmark666]

2:50

he also imagined and ask himself a question

that if apple tree was on the moon,does apple fall?

[MrZeus7]

GRAAAAVITYYYYYYYYYYYYYY!!!!!!!­! ;-)

[xXSparky117Xx]

I like to imagine gravity as a universal magnet for everything, it's fun to play with.

[reznoire]

Woot

[FersotJ]

newton invented the doggy door... definitely the smartest guy ever.

[lpbug]

fifth

[2tchins]

Khan Academy rocks!!!!! Loving this video. :D

[nitrorev386]

wait... what the F*$k is gravity?

[mattswimmer1]

YAY PHYSICS =D

[mrtnHD]

Interesting as always, love khan academy :)