Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > General Science Forums > Physics Forum
Register Search Today's Posts Mark Forums Read

Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


orbital mechanics question - can anyone help me ?

orbital mechanics question - can anyone help me ? - Physics Forum

orbital mechanics question - can anyone help me ? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 11-09-2003, 08:59 PM
steve mew
Guest
 
Posts: n/a
Default orbital mechanics question - can anyone help me ?



If :

1) A body at rest on the ground experiences a force due to gravity of 1g
and

2) A body traveling at 29,739,569.6 ms-1 @ altitude 150,000m experiences an
effective downward force of 0g due to escape velocity



then what effective gravitional force exists for a body at say 100,000 m
altitude and 2000 ms-1 ?



What is the formula to work this out ?



Can anyone point me in the right direction ? Any help greatly appreciated.











v = 29739569.6 ms-1




Reply With Quote
  #2  
Old 11-10-2003, 03:30 AM
tadchem
Guest
 
Posts: n/a
Default orbital mechanics question - can anyone help me ?


"steve mew" <[Only registered users see links. ]> wrote in message
news:sUxrb.16625$[Only registered users see links. ]...
an

Wrong. The body at 150 km altitude experiences a downward "force" due to
gravity ( personally prefer to think of it as curvature of space). Because
of its velocity, it is moving away from the earth even as the earth's
gravity moves it towards the earth. When these effects are in balance, we
say the object is "in orbit." The *net* force may be 0, but thet does not
mean that the individual forces are zero.

To solve the problem in old-fashioned Newtonian mechanics, the "force" of
gravity varies as 1/r^2 (from Newton's Law F = -G*M1*M2/r^2), so for two
given objects at two different distances (m1 and m2 are the same r changes)

F1 = -G*M1*M2/r1^2
F2 = -G*M1*M2/r2^2

so

F2/F1 = r1^2/r2^2

OTOH, the "force" with which the circular motion is throwing the smaller
object outwards is given by

F = m*v^2/r

where v is the velocity perpendicular to the radius.


Reply With Quote
  #3  
Old 11-10-2003, 05:36 AM
steve mew
Guest
 
Posts: n/a
Default orbital mechanics question - can anyone help me ?

Thanks for the clarification and I am sure what you have given me is very
useful but I am not sure what to do with it. (been about 9 years since I was
ina physics class)
I need a rearranged equation to give me the net effect of force in the y
plane as a projectile is travelling in a decaying orbit.
How do I calculate y force given speed and altitude ?

Thanks

s


"tadchem" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
Because
changes)


Reply With Quote
  #4  
Old 11-10-2003, 09:58 AM
tadchem
Guest
 
Posts: n/a
Default orbital mechanics question - can anyone help me ?


"steve mew" <[Only registered users see links. ]> wrote in message
news:gtFrb.17928$[Only registered users see links. ]...
was

It's been about 20 years for me.


If the orbit is decaying, then there is something stealing angular momentum
and energy from the motion. This is called "friction" or "drag."


You need to know more, such as the drag coefficient. Given speed and
altitude you can calculate the energy and the angular momentum. Without
drag, the orbit will remain stable because angular momentum and energy are
conserved - i.e. they will not change. The motion and gravitation will stay
in balance.

To calculate the rate at which the object is "falling" - presumably the rate
at which the orbit is decaying, you need to know something else about what
is going on, such as what fraction of the energy or angular momentum is lost
in a given unit of time.


Tom Davidson
Richmond, VA


Reply With Quote
Reply

Tags
mechanics , orbital , question


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Moving Dimensions Theory Book Due Out in Fall 05--Very Rough Draft: 4th Dimensions Expanding Relative to 3 Spatial Dimensions jollyrogership@yahoo.com Physics Forum 64 03-31-2012 10:24 AM
Simply put, MOVING DIMENSIONS THEORY is THE NEW MODEL: http://physicsmathforums.com drelliot@gmail.com Physics Forum 0 08-29-2006 06:32 AM
Moving Dimensions Theory!! Rock On!! drelliot@gmail.com Physics Forum 1 07-06-2006 05:19 PM
THE ETHER, QUANTUM MECHANICS & MODELS OF MATTER Laurent Physics Forum 6 01-09-2004 11:14 PM


All times are GMT. The time now is 05:14 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.16919 seconds with 16 queries