Gravitation (part 2)

[willbirful]

i enjoyed this vid

[sprattysy]

some sweet info here

[rodswebdesign]

brilliant video

[Kricardose]

I am very happy to see the vidoe A little bit more on gravity after you give this

[bebeheuy]

I Love The Video A little bit more on gravity It Can Increase My Knowledge

[Mjhond]

Steady I Really Like This Video A little bit more on gravity

[HeyRuka]

Gonna need to watch these again...I should stop staring out the window and daydreaming. stupid window...

[00Gravity]

now i understand how strong must have been the little prince living on such a small planet :D

[Chantheman5]

to runnjump101 shut up

[MrEmir93]

can you prove the gravitation equation???? plz

[Primo123321]

Correct me if I'm wrong. Our weight in Jupiter is greater than Earth.

Therefore Our weight in Earth is greater than Small Earth.

W on Jupiter > W on Earth; W e > W small e.

[gunnergrant12]

@Primo123321 no way in hell. As he showed you in this and the last video the weight is the force between you and the massive object which is decided based on the MASS of the objects, NOT the size of them.

[mmoises321]

@Primo123321 your mass would be the same, he is using mass

[ewok100]

@Primo123321

Mass and weight are the same. Mass is a constant, but i guess weight can be described as mass due to the force of gravity on you, if that makes sense.

[ewok100]

@Primo123321

Mass and weight are not the same. Mass is a constant, however weight is due to the force of gravity. w=mg

[mohtaprashant]

lol cool end

[aznswaggerpimp]

LOL

"some gravity towards eachother. it's actually a little romantic"

[FurlowFurlow]

@aznswaggerpimp They would float to each other, ha.

[vinnienauta]

I LOVE YOU!!! YOU SAVE MY LIFE!!

[tadm123]

brilliant

[pythonAndCpp]

Thank You SOOO MUCH... Our Physics teacher is an idiot, I am now ready for my %!@# unit test, Thank you !!!

[Ambriz745]

You never cease to impress. Thanks again.

[masterslayer817]

He said he didnt want to disclose his mass but in an earlier video he said he wieghed about 150 pounds. Just sayin. Great vid though, thanks!

[Emi11235]

The small planet should be called Raxacoricofallapatorius.

[WOWFPS]

/watch?v=391txUI76gM&feature=c­hannel

its called introduction to newtons law of gravatation

[datzfast]

hello khan academy i hate math so here is my question : IMGANARY hole through the earth , question do the gravity vectors cancel out somewhere near the middle? its a YES , NO answer is the correct answer.

[IowaEngineering]

please can u speak a bit louder...i can't get wat ur speaking.

[pollyproof13]

What would happen if everybody on earth jumped at one time?

[Hilrond]

If a smaller planet means that there is a stronger gravitational pull because their centre of masses are closer then why is there less gravity on the moon, not more?

[jewbinson]

@Hilrond Because the moon is less dense than the Earth, and far less heavy than Earth

If you work it out using facts and figures from wikipedia, you will find that the gravity on the moon is roughly 6 times less than that on Earth

[lucasmontec]

"I love you" - from Brazil dude! You just saved my day..... again!

Your job is amazing... you are a good person!

[jimilinuxguy]

Khan, thank you for all that you do. These videos are very helpful, even at the college level. Especially if you find math to be unintuitive.

[SBUCompEngr]

I have a hard time solving this problem...

How far above the Earth's surface will the acceleration of gravity be half what it is at the surface? Can you help please?

[mitchcookskate]

well if you know that acceleration will be half, that is sorta of the same as saying the force of gravity will (Fg) will be be half, using the rule Fg = GM/r^2, if you know that Fg has doubled then it means that r^2 has also doubled sicne Fg and r^2 are inversly proportional, ie the further you get from the surface (the bigger r) the smaller the Fg (acceleration) is, hence your distance will be whateva the square root of 2 is (1.41 somethign) because r is squared

[Tsardoz]

Dont like this one Sal. If you talk about mini earth one would expect it to have the same density as Earth. Since V = 4/3*pi*r^3 for a sphere it has 1/8 the mass of earth, not 1/2 as you state. This would then make the force due to gravity just 1/2 that of earth, not twice.

[r3an1maXion]

hmm dont think the guy meant it as mini earth...he meant it as another planet with 1/2 the rad of earth and 1/2 the mass of earth

[Extralucas]

C'mon it's simplified for the sake of didactics.

[LulJam]

haha it's kind of romantic.

thank you for the video

[realisoph]

Nice vid... however, there's no "pull" in my world.

[SuperSneakyPanda]

i love you.

[physivic]

7:10 "earth won't be doing a lot of moving." lol dude is truly funny

[johsehf]

dum question but.. why do people float all over the moon if it's radius and mass is much smaller than the earth's.

[ureasonnable]

Because the moon gravitational force is so much weaker than the earth gravitational force. that is the reason people float on the moon but not on earth.

[Paulorific]

Do the calculation yourself:

Moon's Mass: 7.3459x10^22 kg

Moon's Radius: 1737.5 km

[megaelliott]

I have just done so and I have come to the conclusion that Moon gravity acceleration=1.623m/s^2(rounde­d). Is that correct?

[Paulorific]

Exactly right :)

[HumanStrategy]

The moon's gravity is about 1/6 of what it is on Earth due to it's mass.

[TagaPasay]

Since the radius of the moon is much smaller than earth's .. The force of the gravity will be much smaller than earth's gravity and that's why astronauts float all over the moon surface..

[laputahayom]

that is not complicatedly true it radius is smaller but that actually has the opposite affect and increases the moons gravity but it's mass is still to low to compensate.

[PinkyFromPK]

Your question is totally valid.

And I believe he has answered your question in this very same video.

Anyway, I will try to answer again:::::

If the moon is made up of all IRON with its current size(diameter), then you will never be able to fload on moon's surface.

Even it would make walking and running difficult for you.

So the size(radius) is not the only factor here; MASS is also playing its role.

[RyuDarragh]

Well, chingensaiXX, barring a video, think about it.

Standing on a sphere, the pull is not perfectly collimated. In otherwords, some of earth to either side of you is pulling on you, too.. sideways (at an angle).

As you fall *into* the earth down that hole, more of the earth is pulling sideways, so the downward pull becomes less and less.

You would fall with lower and lower acceleration until you hit dead center, where you would be at 0G.. all pull is outward.

[laputahayom]

just a Q's what would hapeng to your volacity would it slow down then stop at the center

[crashforward2002]

" P E R F E C T ! ! ! "

[chingensaiXX]

Thank you for all of your videos! This helped me reinforce many concepts.

I have a request for a video, as I was introduced to the concept of "drilling a hole in the Earth" and the effects of the force of gravity if something were to be dropped down the hole. Could you make a video on this concept of "a hole in the Earth"?

[chopperhead2011]

I love physics!!!

[gili192]

i was searching for the first part of the video, but i couldn't find it. can someone send me the link (posting it here please)

[khanacademy]

All of the physics videos are in order in the physics Playlist.

[Waranle]

Thank you this great video, Khan are you from Pakistan?

[khanacademy]

My family is Bengali, but I was born in New Orleans

[Nazmus1992]

@khanacademy you are Bangali! That's really cool!

[msms47]

@khanacademy hey then why is the moon have 6th less gravty than eath when the raidus is smaller ?

[Mcoolshi]

@khanacademy that makes you of Indian origin?