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Name: rk
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: 1999 - 2000


Question:
How does it explain that we have to do only 190,000 miles on way to moon at speeds like 225,000 miles an hour or so and beyond that moon's graVITY PULLS IN.pLEASE EXPLAIN BASED ON NEWTON'S LAW OF GRAVITY.


Replies:
The book by ABC science editor says,we have only to worry about first 190,000 miles,rest 50,000 miles are easy to cover since Moon's gravity pulls in the mooncraft.I am asking How Newton's laws come in this;how the relation m1xm2/r2 plays in this.Thanks.RK VARMA,PE.

Newton's Law of gravity is F =G mM/R^2 , where G is the gravitational constant, m and M are the masses of the bodies being considered, and R is the distance separating the masses m and M.

Gravity obeys the law of superposition, i.e. the total effect of gravity on a body, say M, is the sum of contributions from all the other masses in the Universe. Of course, practically, the distance R is so large that only a few bodies have an effect on M. So the net force of gravity on a mooncraft M is the resultant of of two major forces: Fearth in one direction and Fmoon in the opposite direction. All the other planets, stars, etc. have only a minor effect on M.

Once the mooncraft reaches a certain distance from the earth, Fmoon Fearth so the tug of the earth is smaller than that of the moon, so the craft can just "coast" the rest of the way. In fact, it will accelerate as the craft approaches the moon in a fashion analogous to what happens to a rock when it is thrown up in the air. It goes up so far then falls back (coasts) to earth.

This gravitational attraction is used to "slingshot" a rocket around the moon and off into outer space.

Vince Calder



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