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## My question is that how we knew about the mass of Sun?

i was thinking about the rotation of the heavenyl body and friction.

i dint get it that how friction is not affecting the rotation of the planets? and why there is rotation for these bodies for eternity?

for example, why Earth revolve on its own axis?

due to Gravitational Law>..

would any of you pleas help me to know that how we knew that there is mass of Sun?

m i sounding absurd?

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• #### Thomas Reddy

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May 29 2012: Force of gravity has been determined in the lab. We can detect it's interaction on small particles, and can determine its effect by observations of objects on a large scale.

We have a very great understanding of the effect gravity has on matter. We know that all matter is attracted to all other matter. We can tell that the force shrinks dramatically as a function of distance between the objects. We can make extremely accurate predictions about the force of gravity, and can say how it effects systems with great precision. From this, we have can infer the mass of the sun, and other objects in the night's sky.

If you want to know "How" gravity works (like what are those invisible strings holding us to the earth, and holding the earth in orbit around the sun?), that's a harder question. There are some theories that show great promise but haven't yet been proven. But to understand those theories in great detail, it would be helpful to have a greater understanding of mathematics and physics.

As for the friction issue, because the amount of "stuff" in space is so little, the force of friction is so close to zero, it has next to no effect.
• #### Peter Law

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May 26 2012: Hi Simply.
The rotation of the earth is slowing down. This is due to the moon pulling on the oceans & causing the tides. It also has the effect of accelerating the moon, which is gradually moving away from us. So our days are getting longer all the time.
The sun is also getting smaller as it's fuel is used up, not sure about it's mass.
:-)
• #### Noor Afsha

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May 26 2012: Thanks Peter

what kind of fuel is in there? are we rally sure its fire that is producing heat and light for us?

if earth is slowing down.....would it stop rotating one day?
• #### Stewart Gault

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May 26 2012: It's not the kind of fire you might think of, in the sun it's nuclear fusion of hydrogen atoms which releases so much energy that it produces the light and heat through the electromagnetic spectrum which is the energy released by these particles coming together
• #### Stewart Gault

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May 26 2012: Also the Earth won't stop spinning, once the moon orbits earth at the same speed the earth rotates there won't be anything slowing the Earth down anymore, but this takes a few billion years.
• #### Jerry Fausta

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May 25 2012: Will to have friction you would need to have something acting on that object. But seeing that space can be bent by the stars and planets mass there can not be friction. Its all in the theory of relativity.
• #### Noor Afsha

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May 26 2012: HE Jerry.... what is causing the gravity?
• #### Stewart Gault

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May 26 2012: Gravity is the effect of mass, things with a larger mass attract those with a smaller mass, this is created by matter's currently theoretical effect on the Higg's Field
• #### Gerald O'brian

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May 27 2012: those with a smaller mass attract those with a larger mass as well
• #### Thomas Reddy

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May 29 2012: Specifically, all objects with mass are attracted to ALL other objects with Mass. Closer and more massive objects have a more dramatic effect. The force of gravity is generally a very weak one, compared to the other known forces (electromagnetism, weak nuclear, and strong nuclear).