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Gravity and Laws
Name: Unknown
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: 2000-2001
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.
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.
Replies:
Real simple. The magnitude of the force acting on the spacecraft from the
earth's gravity will be GmSmE/(rSE)^2, and the force from the moon's gravity
will be GmSmM/(rSM)^2. Here, G is the gravitational constant, mS is the mass
of the spacecraft, mE is the mass of the earth, mM is the mass of the moon,
rSE is the distance from the spacecraft to the earth, and rSM is the
distance from the spacecraft to the moon. These forces will be in the
direction toward the earth and toward the moon, respectively. The total
force on the spacecraft is the sum of the forces from the earth and the moon
(ignoring forces from objects like the sun, Mars, etc...). If the
spacecraft is on a line between the earth and the moon, these two forces
will act in opposition to each other. When the magnitude of the force from
the moon is greater than the magnitude of the force from the earth, then the
moon will pull the craft in. By substituting into the formulas the proper
values for mE, mM, and the distance from the earth to the moon, you should
be able to calculate this distance.
Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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