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# Tag Archives: planet

## How does the atmosphere rotate with the Earth?

How does the atmosphere rotate with the Earth? (Asked George) ## Why moon does not fall to Earth?

The moon does not fall to earth because of its tangential velocity. The following video explains it well. ## A question from Gravitation.

“Sun have high gravitational energy ,then why planets of solar system doesn’t colloid with sun?”

“The planets are moving around the sun and the gravitational force is used in providing the necessary centripetal force (The force required by a body to move in a circular path). As long as the planets are in motion, they will not move towards the sun. A similar explanation hold good for moon going around earth also.”

## Acceleration due to gravity problem

A body weighs 30 kg on the surface of the earth how much would it weigh on the surface of a planet whose mass is 1/9 the mass of earth and radius is half of that of earth? Weight on earth = 30 kg wt = 30 x g N

g on new planet, g’ = GM’/R’2=(4/9)g

Therefor weight on the new planet will be equal to 4/9 times its weight on earth

(Whereas the mass will be the same)

## why earth moves in an elliptical orbit instead of circular one?

why earth moves in an elliptical orbit instead of circular one?

Ans: Please note that ELLIPSE is the more general form for an orbit and CIRCLE is a speacial case of ellipse.

So, it is more general way of saying that the orbits are elliptical. If it were circular, we would have more trouble explaining why they are perfect circles.

The situation where the Sun, for instance, would be exactly in the center of a perfectly circular planetary orbit couldn’t happen in our Solar System since there are other planets that would gravitationally affect the orbit and cause it to be immediately non-circular by pulling the object to one side or the other.  Any other stable orbit type than a perfectly circular one turns out to be an elliptical orbit.

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