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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.

English: Diagram of orbital motion of a satell...

The initiative http://lunarscience.nasa.gov/ask-a-scientist/ by NASA will answer all your doubts on moon.

Is the gravitational force between moon & earth are equal ?

Newton's law of universal gravitation for two ...
Newton’s law of universal gravitation for two bodies. This law governs gravitational forces in the Earth. (Photo credit: Wikipedia)

Is the gravitational force between moon & earth are equal ?

If the question is- “Is the force exerted by earth on moon is equal to the force exerted by moon on earth?” then the answer is “Yes

I hope that more questions will follow.

Please post your questions as comments to this post.

  • Comparison of charge and mass

Parallax Method to determine the distance of stars



Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

Astronomers use the principle of parallax to measure distances to celestial objects including to the Moon, the Sun, and to stars beyond the Solar System.

See the animation below to understand the parallax method for determining the stellar distances

Find more information here



Aswin Ramesh Asked (via email)
is it the same method that we use in trigonometry ?
Parallax is a different concept, though we are using the principle of trigonometry to solve problems based on it.

Questions received and waiting to be answered

Sreeda Asks

  1. Why are we not feeling Earth’s rotation while it is actually happening {1674.4 km/hr at the equator}?
  2. Our sound varies while communicating through a telephone. Why?
  3. Why is it more neat when we tear a sheet from the newspaper vertically and rough when torn horizontally?
  4. Will we be able to see stars during day time on the moon?
  5. Why do planets move in elliptical paths and not in circular ones?
  6. At what depth do Jupiter quakes occur?
  7. Charan Asks

what is the difference between a atomic and a nuclear bomb?

sly nikie asks

what is crystal cleavage and what does it state about the nature of matter?

A question from Gravitation.

Prince Patel Asked:

“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.”

Weight and inertia on moon

Say True or False; An object on the Moon weights 1/6 of what it weights on the Earth. Therefore, the object has less inertia on the Moon.( Justify your answer)

Answer: The statement is false.

Inertia depends on mass and not on weight. The weight on moon is less not because of a decrease in mass, but due to the decrease in the acceleration due to gravity on the surface of moon.

Inertia depends on mass and there is no change in mass when a body is taken to moon. Therefore the inertia of a body is same on moon as that on earth or anywhere else in the universe, even in a gravity free space.

Moon Landing

It is said  that there is no atmosphere in moon therefore no air but when Neil Armstrong landed on moon first and hosted the us flag it flapped. how can this happen??

(See the photograph below)
The photograph below shows the photographs of flag taken from two different angles at slightly different times. Watch the curls and curves on flag. They have not changed
Lunar landing flag

Vishnu Comments: “hosting could have sent a disturbance up the pole and thru the flag. Does it flap? we cant say that from a fotto. in moons surface, if we keep the flag with curls, the curls stays there.  is there a vdo of flapping? After all its not worth discussing a lot over this”


Past Human Lunar Expeditions

Apollo 8  (21-27 December 1968)

Frank Borman, William Anders, James Lovell

Apollo 10 (18-26 May 1969)

Thomas Stafford, Eugene Cernan, John Young

Apollo 11 (16-24 July 1969)

Neil Armstrong, Edwin Aldrin, Michael Collins

21h 36m / 2h 31m / 21.6 kg

Apollo 12 (14-24 November 1969)

†Charles Conrad, Alan Bean, Richard Gordon

31h 31 m / 7h 45m / 34.3 kg

Apollo 13 (11-17 April 1970)

James Lovell, Fred Haise, †John Swigert

Apollo 14 (31 January – 9 February 1971)

†Alan Shepard, Edgar Mitchell, †Stuart Roosa

33h 30m / 9h 21m / 42.8 kg

Apollo 15 (26 July – 7 August 1971)

David Scott, †James Irwin, Alfred Worden

66h 54m / 19h 6m / 76.7 kg

Apollo 16 (16-27 April 1972)

John Young, Charles Duke, Thomas Mattingly

71h 2m / 20h 14m / 94.5 kg

Apollo 17 (7-19 December 1972)

Eugene Cernan, Harrison Schmitt, †Ronald Evans

74h 59m / 22h 2m / 110 kg










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