

Moon's Distance and Gravity
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
Click here to return to the Astronomy Archives  
Update: June 2012

