Interesting questions about our Universe...

[2gud]

Thinking and finding answers about Universe gives me tremendous satisfaction, and adds more meaning to my life.

I am sure all of us have some or other question about the Universe and some of us have answers to some of the tricky questions. In another thread I talked about how tides are caused in the ocean by moon's (as well as sun's) gravity on earth. Thinking about it I thought why not start a thread, in which I will put all the interesting questions I had since childhood, which no one including my teachers could answer me at that time, but I have found them by myself overtime.

To start:

Question 1: The force of gravity of Sun on Moon is stronger than the force of gravity of Earth on Moon. But why does Moon still orbit Earth, why can't Sun snatch it away from Earth?

I know the answer, but I want to see what you guys would come up with.

I also have a lot of other interesting questions in my sleeve!

http://primetimes2.com/moon-earth-sun.gif

Artistic rendering of Sun, Earth & Moon system (not to scale!)

[Sane Less]

Ten reasons why the sun can't snatch moon away from earth:

1. The moon loves earth
2. Love of sun will soon burn out
3. Love of sun will leave moon all ravaged and spent
4. Earth's love is soft and cool
5. Earth is way prettier than sun. Nice blue and green, compared to sun's bright orange
6. You know people who like bright orange colors, have no respect for love... valentine's day :wink: :wink: (no offence, Shivsanki pai;))
7. The moon can have nightly visits from the earth, it is so close
8. All the sun does is sing, "Tu pyar hai kisi aur ka, tujhe chahata koi aur hai"

can't... somebody... come up with the remaining 2 reasons.

[Napolean]

Thinking and finding answers about Universe gives me tremendous satisfaction, and adds more meaning to my life.

I am sure all of us have some or other question about the Universe and some of us have answers to some of the tricky questions. In another thread I talked about how tides are caused in the ocean by moon's (as well as sun's) gravity on earth. Thinking about it I thought why not start a thread, in which I will put all the interesting questions I had since childhood, which no one including my teachers could answer me at that time, but I have found them by myself overtime.

To start:

Question 1: The force of gravity of Sun on Moon is stronger than the force of gravity of Earth on Moon. But why does Moon still orbit Earth, why can't Sun snatch it away from Earth?

Artistic rendering of Sun, Earth & Moon system (not to scale!)
Are you sure about that fact,2gud?If yes,I really wonder why moon keeps rotating about earth!!
Give us the answer.Thx.

[tantric_yogi]

BhaYa ... 6 years is witness ... I never speak sense but today I try ... for you.

I watch a movie long time ago. Raj Kapur's son (Randhir ?) a good boy. He save MoonMoonSen from goondas. MoonMoon love Randhir very much. Randhir's gravity very strong on girl. But one day Randhir (sun) got to go away to far far away to London. Although Randhir's (sun's) gravity on MoonMoon (moon) is very stronger still distance is very long ... comes Gulshan Grover (earth) ... Grover (earth) bad boy very little gravitational strength but he live in the same city as MoonMoon. So although Grover bad boy but because he is close to Girl so girl stay close to him and become friends. Randhir Kappor gravity very strong but cause he live far far far away got screwed.

Something like that? ;)

[Napolean]

BhaYa ... 6 years is witness ... I never speak sense but today I try ... for you.

I watch a movie long time ago. Raj Kapur's son (Randhir ?) a good boy. He save MoonMoonSen from goondas. MoonMoon love Randhir very much. Randhir's gravity very strong on girl. But one day Randhir (sun) got to go away to far far away to London. Although Randhir's (sun's) gravity on MoonMoon (moon) is very stronger still distance is very long ... comes Gulshan Grover (earth) ... Grover (earth) bad boy very little gravitational strength but he live in the same city as MoonMoon. So although Grover bad boy but because he is close to Girl so girl stay close to him and become friends. Randhir Kappor gravity very strong but cause he live far far far away got screwed.

Something like that? ;)
when 2gud says force of gravity,I think he is saying that taking distance into account as well.So even at this distance Sun exerts greater force on moon than earth does.
Does not seem true to me but since 2gud is so confident about it,I will better hear his explanation.

[2gud]

Here are some figures:

Mass of the earth ~ 6 x 10^24 kg
Earth-moon distance ~ 384,000 km
Mass of the sun ~ 2 x 10^30 kg
Sun-moon distance: ~ 150,000,000 km

The sun's gravitational pull on the moon is proportional to
2 x 10^30 / (1.5 x 10^8)^2 ~ 8.8 x 10^13
The earth's gravitational pull on the moon is proportional to
6 x 10^24 / (3.84 x 10^5)^2 ~ 4 x 10^13

So you see sun pulls moon twice as strongly as earth does

[tantric_yogi]

Here are some figures:

Mass of the earth ~ 6 x 10^24 kg
Earth-moon distance ~ 384,000 km
Mass of the sun ~ 2 x 10^30 kg
Sun-moon distance: ~ 150,000,000 km

The sun's gravitational pull on the moon is proportional to
2 x 10^30 / (1.5 x 10^8)^2 ~ 8.8 x 10^13
The earth's gravitational pull on the moon is proportional to
6 x 10^24 / (3.84 x 10^5)^2 ~ 4 x 10^13

So you see sun pulls moon twice as strongly as earth does


I believeing to you and your figures ... I thought you were going to be sharing to us your findindings as to why Moon staying faithful to earth and not running vunning away to join lover Sun even though Sun's attraction is much stronger compared to that of earth which I think has to do with distance? You promised to share your personal findings ... noh?

Nepalibhai ... what 2Gudbhai says has rings of truth surrounding it but you as well know that it got to be doing with distance ... and so far 2Gudbhai dealing with gravity but not the distance which is what matters when answering his question in post number Yone. I think. But what do we know ... both LLKC.

[2gud]

If a gravitationally bound system like Earth and Moon have to separate by a force external to this system (like Sun's gravitational force), it is not the intensity of Sun's force on any particular body - Moon or Earth that counts. So even if Sun pull's Moon twice as stronger than that of Earth on Moon, still the Moon does not need to separate from Earth.

In fact, one can say both Earth and Moon are nearly equally pulled by the Sun, and because of the pull both are accelerating nearly equally towards Sun. So Sun is not pulling one from the other, but pulling them more or less equally together.

It will separate only if the tidal forces of Sun on Earth-Moon system trying to pull away Moon from Earth are stronger than the gravitational force of Earth on Moon. Due to Sun's gravitation both Earth and Moon are accelerating towards the Sun, it is the difference in these accelerations, i.e., the net acceleration of separation of Moon from Earth due to Sun (in other words tidal acceleration of separation of Moon from Earth) that counts. This should be greater than the acceleration due to gravity that binds Moon to the Earth.

Tidal force of Sun separating Moon from Earth = Mass of Moon * ( accln due to gravity of Sun on Moon - accln due to gravity of Sun on Earth).

This tidal force should be greater than the gravitational force that binds the Earth and Moon system, for the Moon to be plucked away from Earth and settle into its own orbit like another planet.

It is not, so Moon is gravitationally bound to the Earth + Moon system which together orbit the Sun.

[Napolean]

2gud,thanks for all the facts.
if that is the case,then it has got to do with components of forces.
What I mean is that Earth moon force may not be exactly opposite to the Sun moon force.They may at angles to each other and that is where earth moon force may be greater.
Well, I don't know the exact answer as I have already said ....I am just trying to make sense out of it.
As TY said,once LLKC always a LLKC.

[2gud]

2gud,thanks for all the facts.
if that is the case,then it has got to do with components of forces.
What I mean is that Earth moon force may not be exactly opposite to the Sun moon force.They may at angles to each other and that is where earth moon force may be greater.
Well, I don't know the exact answer as I have already said ....I am just trying to make sense out of it.
As TY said,once LLKC always a LLKC.
It is quite easy Napolean bhai, I can summarize what I wrote above in simple words.

Both Earth and Moon are pulled by Sun, because of this both Moon and Earth accelerate, but the difference in this acceleration is not as strong enough as to overcome the graviational force that binds the Earth-Moon system and separate them.

Also understand that acceleration just doesn't only mean increase in velocity, it can also mean change in direction of velocity, in other words moving in a curved orbit is also acceleration

[Chhota baccha]

I think Moon is being pulled by gravitational force of the Earth, other Planets as well as of the Sun.... thts why the Sun can't snatched it from Earth..... but i m not so confidant... so waiting for answer.....

[2gud]

I think Moon is being pulled by gravitational force of the Earth, other Planets as well as of the Sun.... thts why the Sun can't snatched it from Earth..... but i m not so confidant... so waiting for answer.....

OK again... I will now make it as simple as it can...

Suppose you are pulling two persons with a rope, if you pull them equally strong then both of them move towards you without the distance between them increasing/decreasing. They can move away from each other only if you pull one of the person more stronger than the other.

When I said, that Sun pulls the Moon twice as stronger as Earth pulls Moon, it is also the fact Sun is pulling the Earth too equally strongly. So Moon and Earth can only separate if they are pulled with much different strengths, which is not!

[vyomkeshsaxena]

well letz c my theory..

just like artificial staellites are launched from earth and they orbit erath and are not attracted towards sun...so to speak..according to one theory..moon was ripped out from earth and got placed in orbit :D :D

well what i remember from 10th standard CBSE books...force of gravity is given by

f- G*m1*m2/r^2

where G's value..if iem not mistaken was 6.63*10^-34 N/m or n/m^2 ( confused ab the unit)

m1= mass of 1st body and m2- mas of second body
r= distance between two bodies

iem sure the answer must be lying in this formula..pretty busy right now for calculation...but since F is inversely proportional to 'r' value..so to speak...less "r" i.e moon n earth means more gravitaional force...

newaz...

[Chhota baccha]

...... it is also the fact Sun is pulling the Earth too equally strongly. So Moon and Earth can only separate if they are pulled with much different strengths, which is not!
I think....... gravitational force between the two bodies varies directly proportional to product of their masses and inversely proportional to square of distance between them....so cant understand how the Sun will pull the Earth and Moon with equal force??? If Newton's this law is correct then the gravitation force between Sun and Moon will be more than the gravitation force between Sun and Earth.....Further, the position of Moon around Sun is not static... its distance from Sun varies depending upon the position of the Moon.....distance of Moon from the Sun will be more when the Earth will come between Moon and Sun......koi eclips hota hai us time.....shayad luner ya koi aur..... So 2gud uncle want calarification......

My thinking may be wrong....... but maine ye soch kar bola tha ki all celestial bodie have their gravity..... nd only becose of this they are able to move in their fixed orbit..... they all attract each other...... and also they are not in a lenear position........ so they attract each other from various distance and various direction........ I may be wrong..... but want to know......shall be gratefull.........

[HarHarMahaDev]

well letz c my theory..

just like artificial staellites are launched from earth and they orbit erath and are not attracted towards sun...so to speak..according to one theory..moon was ripped out from earth and got placed in orbit :D :D

well what i remember from 10th standard CBSE books...force of gravity is given by

f- G*m1*m2/r^2

where G's value..if iem not mistaken was 6.63*10^-34 N/m or n/m^2 ( confused ab the unit)

m1= mass of 1st body and m2- mas of second body
r= distance between two bodies

iem sure the answer must be lying in this formula..pretty busy right now for calculation...but since F is inversely proportional to 'r' value..so to speak...less "r" i.e moon n earth means more gravitaional force...

newaz...


If all this shit is true....then why doesnt earth collapse into the sun?

I believe there is are centrifugal forces involved. Multiple forces are balancing themselves out. It is not just gravity.

[Chhota baccha]

Question 1: The force of gravity of Sun on Moon is stronger than the force of gravity of Earth on Moon. But why does Moon still orbit Earth, why can't Sun snatch it away from Earth?



2Gud uncle mujhe pata hai u know the answer….but shayad aap kuch busy ho so time nahi mil pa raha hai aapko reply karne ka…….waited 2Gud days……sannata chaya hua dekha har pal is thread me……koi samne nahi aa raha aapke question ko solve karne ko…….so let me try to solve this or to try to end this question……

I hv given earlier the indication that all celestial bodies have their own gravity..... nd only becose of this, they are able to move in their fixed orbit…..so it is the common sense that why Moon orbits around the Earth and not around the Sun….

Ab main aapke question pe aata hu…..Haath kangan ko aarshi kya aur padhe likhe ko pharsi kya……. Ek kahawat hai idhar…. You have the masses of earth and sun…. I m giving u the mass of moon (approx. 0.012 time of the mass of earth)….. you have the distance between sun and earth, sun and moon & earth and moon……… but u hv the wrong formula (I think so becose I know that gravitational force between the two bodies varies directly proportional to product of their masses and inversely proportional to square of distance between them)……… Vuyomkeshbakshi uncle has given u the correct formula…… so try karo…… aapko khud hi pata chal jaega ki which force is stronger? the force of gravity between Sun and Moon or the force of gravity between Earth and Moon? Aur jab ye pata chal jaega then aapko apne question ka answer bhi mil jaega....

Dhanyavad

[Chhota baccha]

Second simple and interesting question in this thread

Q.No. 2

How may days a Leap Year has??? and Why???

[2gud]

I think....... gravitational force between the two bodies varies directly proportional to product of their masses and inversely proportional to square of distance between them....so cant understand how the Sun will pull the Earth and Moon with equal force??? If Newton's this law is correct then the gravitation force between Sun and Moon will be more than the gravitation force between Sun and Earth.....Further, the position of Moon around Sun is not static... its distance from Sun varies depending upon the position of the Moon.....distance of Moon from the Sun will be more when the Earth will come between Moon and Sun......koi eclips hota hai us time.....shayad luner ya koi aur..... So 2gud uncle want calarification......

My thinking may be wrong....... but maine ye soch kar bola tha ki all celestial bodie have their gravity..... nd only becose of this they are able to move in their fixed orbit..... they all attract each other...... and also they are not in a lenear position........ so they attract each other from various distance and various direction........ I may be wrong..... but want to know......shall be gratefull.........
I have not used the correct words... yes the force of Sun on Earth of course would be stronger than that on Moon, as Earth has more mass and force of gravity is proportional to product of masses...

that is not my point... I should have used the phrase "acceleration due to gravity" instead... accln due to gravity because of Sun at Earth and Moon's location is not much different, the difference in accelerations due to gravity is small, if the Moon has to separate from the Earth (and settle into its own orbit around Sun), this difference should be greater than the acceleration due to gravity of Earth on Moon.

You need to think about it to understand it.

[Chhota baccha]

I have not used the correct words... yes the force of Sun on Earth of course would be stronger than that on Moon, as Earth has more mass and force of gravity is proportional to product of masses...

that is not my point... I should have used the phrase "acceleration due to gravity" instead... accln due to gravity because of Sun at Earth and Moon's location is not much different, the difference in accelerations due to gravity is small, if the Moon has to separate from the Earth (and settle into its own orbit around Sun), this difference should be greater than the acceleration due to gravity of Earth on Moon.

You need to think about it to understand it.

2Gud uncle..... dhanyawad..... i will definetely try to understand....why?? becose i m nothing......and i m here only to learn something from u all....But first question ka answer to ho gaya.....2Gud uncle..... i m feeling that u hv taken my words in a different way.... sach sach batana..... yadi aisa hai then plzzzzzzzzzzzz.... na mera intention aisa kabhi tha... na hai aur na hi rahega..... not only in this thread but also on echarcha..... so plzzzzz try to understand me.... i m here only to learn something.....

[Alibaba]

Also what I think is.. the moon is closer to Earth. Ergo, even though the sun's gravitational force is greater (double) than earth's the actual amount that reaches the moon is probably lesser than earth's gravitational force that reaches the moon! So probably it stays closer to the earth..


Also while browsing through your post.. I came up with a question...

If the sun's gravitational force is so strong.. then how come mercury doesn't stick to it? I mean, mercury is such a small planet.. and the amount of gravitational force that the sun exudes on Mercury is definitely more than that exuded on moon.. :rolleyes:



I wrote this post before reading 2gud's answer/explaination..
Now I know the answer.. thanks 2gud! :up:

[2gud]

I wrote this post before reading 2gud's answer/explaination..
Now I know the answer.. thanks 2gud! :up:

Another simpler way to look at it is like this.. both Moon and Earth are accelerating towards Sun.

For the Earth-Moon system to separate from each other Moon should be accelerating towards Sun more than Earth does, in fact, the difference in Moon's acceleration towards Sun to that Earth's should exceed the acceleration due to gravity of Earth on Moon for the Moon to separate from Earth.

The above difference in acceleration gives rise to what is know as tidal force which arises due to difference in acceleration due to gravity at the nearest and farthest ends of a body (or in case of Earth-Moon system, on Earth and Moon respectively as two extreme ends of the system, say when Moon is betwen Earth and Sun), the more the difference the strong the tidal force. The closer the Earth-Moon system is to the Sun the stronger the tidal force separating them will become, at some point sufficiently closer to Sun, Earth will not be able to hold the Moon.

Earth also exerts tidal forces, if a large body like Moon ventures too close to Earth, at some point (called Roche limit) the tidal forces of Earth on Moon increase to such an extent that Moon will shatter into pieces.

[2gud]

If the sun's gravitational force is so strong.. then how come mercury doesn't stick to it? I mean, mercury is such a small planet.. and the amount of gravitational force that the sun exudes on Mercury is definitely more than that exuded on moon.. :rolleyes:



Yes, Mercury will fall into Sun, if it does not keep rotating fast (even faster than other planets) enough. When a body rotates an outward force comes into play (called centrifugal force) which counter acts the gravitational force of Sun.

Another way to look at it is Mercury (or for that matter Earth and other planets too) are continuously falling towards Sun, when they fall a few meters towards the Sun they also move another few meter in a direction perpendicular, in this way they never ever get any closer to Sun than they actually are. In fact if there were no Sun, Earth or Mercury would have moved in straight lines, the fact that they are moving in curved paths indiccate that they are accelerating, and this acceleratiion always points towards the Sun.

[Shringarey]

Just thought I'd add my 2-penny bit.


The moon really revolves around the sun. But because of a nearby mass (earth), its motion is a little twiddled. How? Well, while revolving around the sun, the orbit makes small loops (each a revolution around the earth).

We are so used to saying that the "moon revolves around the earth", that we believe it to be true. It is true from earths perspecttive. But go far away and you will see that both earth revolves around the sun, and the moon too revolves around the sun. Their proximity to each other twiddles their path, and they ALSO loop around the commom centre of mass between them!


Shring.

[Alibaba]

Just thought I'd add my 2-penny bit.


The moon really revolves around the sun. But because of a nearby mass (earth), its motion is a little twiddled. How? Well, while revolving around the sun, the orbit makes small loops (each a revolution around the earth).

We are so used to saying that the "moon revolves around the earth", that we believe it to be true. It is true from earths perspecttive. But go far away and you will see that both earth revolves around the sun, and the moon too revolves around the sun. Their proximity to each other twiddles their path, and they ALSO loop around the commom centre of mass between them!


Shring.
Hmm.. much simpler explaination! :D :up: I like such stuff... stuff that I can understand! :D