Physics Help Forum The path of Earth about sun

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Jan 30th 2014, 01:04 AM #1 Junior Member   Join Date: Jan 2014 Posts: 15 The path of Earth about sun H!, Im confused about calculate this problem plz solve this for me with second law of newton.
 Jan 30th 2014, 06:10 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,352 Newton's 2nd Law for a body with constant mass is the well-known formula: Newton's law of gravity for the force acting on body m in orbit about M: where r_hat is the radial unit vector pointing from mass M to m. Set these equal, and the motion of the orbiting body (small m) is: For a circular orbit of radius R you can replace the acceleration vector using: and from that derive a formula for the period of the orbit versus orbital velocity and mass M. Not sure what else you're looking for. Last edited by ChipB; Jan 30th 2014 at 06:22 AM.
 Jan 30th 2014, 09:46 AM #3 Junior Member   Join Date: Jan 2014 Posts: 15 im locking for path equation of earth about sun.i know it is a Oval.but i want its equation.
 Jan 30th 2014, 11:48 AM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,352 The general formula is: where l = the angular momentum of the orbiting body, which equals: and 'e' is the eccentricity of the orbit. For Earth these parameters are: l = 2.66 x 10^40 Kg m^2/s m = masss of earth = 5.97 x 10^24 Kg M = mass of sun = 1.99 x 10^30 Kg e = 0.0167 Hope this helps.
 Jan 30th 2014, 01:05 PM #5 Junior Member   Join Date: Jan 2014 Posts: 15 thanks but i want to know how this r is calculate?
 Jan 30th 2014, 02:19 PM #6 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,352 Please clarify your question - are you asking how Kepler's laws of planetary motion can be derived from Newtonian mechanics? If so, the following provides a good derivation. However I don't know your background in mathematics and whether it might be a bit advanced for you. Let me know if this helps: http://en.wikipedia.org/wiki/Kepler%...anetary_motion
 Jan 31st 2014, 02:34 AM #7 Junior Member   Join Date: Jan 2014 Posts: 15 tnx but i dont realize from this. <> yes exact. i want to know this.my background in mathmatics is good.
 Jan 31st 2014, 03:24 AM #8 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,352 Read the section called "Inverse Square Law" on the wikipedia page I cited earlier - it shows how Kepler's Laws are consistent with Newton's law of gravity.
 Jan 31st 2014, 08:03 AM #9 Junior Member   Join Date: Jan 2014 Posts: 15 sorry but i did'nt see that.

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