# What is Planetary motion: Definition and 71 Discussions

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.
For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbital motion.

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1. ### Tusi discovering laws of planetary motion before Kepler?

I was reading about the Tusi couple and read it "as a solution for the latitudinal motion of the inferior planets, and later used extensively as a substitute for the equant". Since the Tusi couple is related to plotting out an ellipse, did Nasir al-Din al-Tusi already discover the laws for...
2. ### A planet of mass M and an object of mass m

HI! I tried to solve this exercise, by assuming that it is an inelastic collision, the planet is spherical, and that the rotation axis is parallel to the z-axis, see the figure attached. (1) before the collision, (2) after the collision.I started by assuming angular momentum conservation, which...
3. ### B What is the relationship between force and distance in planetary motion?

https://www.feynmanlectures.caltech.edu/I_09.html 9-7 "From this figure we see that the horizontal component of the force is related to the complete force in the same manner as the horizontal distance x is to the complete hypotenuse r, because the two triangles are similar. Also, if x is...
4. ### I The centripetal acceleration of the planets in our solar system

Relevant formulae:- Angular velocity in uniform circular motion ##=## ##\omega## ##=## ##\frac {2\pi} t##, where ##t## is the time taken to complete one revolution. Centripetal acceleration in uniform circular motion ##=## ##a## ##=## ##\omega^2r##, where ##r## is the radius of the circular...

29. ### Planetary Motion with satellite

Homework Statement A 20 kg satellite has a circular orbit with a period 2.4 h and radius 8.0×106m around a planet of unknown mass. If the magnitude of the gravitational acceleration on the surface of the planet is 8.0 m/s2, what is the radius of the planet? Homework Equations F =...
30. ### Radius of curvature of planetary motion

Suppose we have a planet of mass m orbiting a larger one of mass M along an elliptical path. If we use polar coordinates with the origin placed on the planet of mass M (focus of the ellipse) then at the instant when the smaller planet is at the point of closest approach we have: \boldsymbol{v}...
31. ### Schwarzschild Solution for Planetary Motion: Find x'i from xi

Schwarzschild solution for Planetary Motion: ##g_{ij}= \left( \begin{array}{cccc} \frac{1}{(1-(\frac{2*m}{r}))} & 0 & 0 & 0 \\ 0 & r^2 & 0 & 0 \\ 0 & 0 & r^2*(sin\theta)^2 & 0 \\ 0 & 0 & 0 & c^2*(1-\frac{2*m}{r}) \end{array} \right) ## where ##m=\frac{G*(Mass of Sun)}{c^2}##...
32. ### Solving Planetary Motion: Mass, Velocity & Energy

Homework Statement A planet with a mass of 8.99·1021 kg is in a circular orbit around a star with a mass of 1.33·1030 kg. The planet has an orbital radius of 1.21·1010 m. a) What is the linear orbital velocity of the planet? b) What is the period of the planets orbit? c) What is the...
33. ### Planetary motion problem

Homework Statement a planet with radius of 12km spins at 520revs/s find: a) avg speed of a point on the planets equator over 2.5 of a revolution b)find avg acceleration on stars circumfrance over 3/4 of a rev c)find distance covered by point on the equator in 1 second d) find displaement...
34. ### Planetary motion problem

Homework Statement At a ertain point between Earth and the moon the total gravitation force exted on an object by both planets is 0. The Earth - moon distance is 3.84 x 10^5 and the moon has 1.2% of the mass of earth. Where is this point located. Homework Equations Fg=GmM/R^2 The...
35. ### Kepler's planetary motion and inverse square law

Hello, The inverse square law of Newton's gravitational force, is it somehow related to each other? I mean to say P^2 is directly prop.a^3. Is it from the third law that the derivation of inverse sq.law of G=M.m/R2 is derived? Thanks.
36. ### Momentum Planetary Motion Problem

Homework Statement Two spheres of mass m and radius r, are released from rest in empty space. The centers of the spheres are separated by a distance R. They end up colliding due to gravitation attraction. Find the magnitude of the impulse just before they collide.Homework Equations Eg= -Gmm/r...
37. ### Gyroscopic effect on planetary motion

Gyroscopic effect on planetary motion! Hi PFians This is my first ever post in astrophysics since I've got very interested in it from last 2 days... I was wondering when Earth rotates about it's axis and at the same time changes it's direction due to revolution about sun...won't it have...
38. ### Kepler's First Law of Planetary Motion

I'm reviewing my old calculus textbook and I stumbled upon a proof of Kepler's First Law of Planetary Motion which uses vector valued functions along with all of the operations to demonstrate the material. I understand the math and how to to DO it but what I am struggling with is why. It goes...
39. ### Center of mass and planetary motion

Why is it that for instance the Earth and the moon orbit their common center of mass? I mean surely the moon feels a gravitational force as though the mass of the Earth were concentrated at its center? If yes, what is that then makes it orbit around their center of mass rather than this point. I...
40. ### [Logarithms]Kepler's third law of planetary motion

Homework Statement Kepler's third law of planetary motion relates P, the period of a planet's orbit, to R, the planet's mean distance from the sun, through the equation log P = \frac{1}{2} (log K + 3log R), where K is a constant. Rewrite the formula as a single logarithm. Homework...
41. ### Exploring Centripetal Force in Planetary Motion

Hi, I know that centripetal force for planetary motion is the same as the force of gravity between that satellite and planet. For example (I know these numbers may be completely unrealistic but just for the sake of easy calculation...) if the mass of the Earth is 1x10^30 kg and the mass of...
42. ### Planetary Motion - Object has both tangential and radial velocity components

Homework Statement A meteor is moving at a speed of 20000mi/hr reltiave to the centre of the Earth when it is 350 mi from the surface of the earth. At that time, the meteor has a radial velocity component of 4000 mi/hr toward the center of the earth. How close does it come to the Earth's...
43. ### Solving Planet A's Semi-Major Axis Ratio To Planet B's

Homework Statement You are one of the first astronomers in a civilization on Planet B in another solar system. With your unaided eye, you follow planet A in the same solar system and note that it never gets further away than 16 degrees from the star (around which both planets orbit). What...
44. ### Planetary Motion HW: Orbit Radius & Speed Around Jupiter

Homework Statement An explorer plans a mission to place a satellite into a circular orbit around Jupiter, the radius of the planned orbit would be R. a)The explorer wants the satellite to be sychronized w/ Jupiter's rotation. Determine the required orbital radius in meters. b) What must...

46. ### Difficult Planetary motion problem

Homework Statement Planet X rotates in the same manner as the earth, around an axis through its north and south poles, and is perfectly spherical. An astronaut who weighs 950.0 N on the Earth weighs 917.0 N at the north pole of Planet X and only 860.0 N at its equator. The distance from the...
47. ### Planetary motion, orbits

Hi I'm a bit confused, I hope you can help. The question is - In the course of their orbits, the distance between the Earth and Venus changes. The radii of the orbits of the two planets are 1.5 x 10e8 km and 1.1 x 10e8 km. If a radio pulse is transmitted from Earth towards Venus, calculate...
48. ### Unraveling the Mystery of Planetary Motion: Mercury & Pluto

why does mercury move with such velocity while pluto is much slower?
49. ### Planetary Motion, calculation of orbital period

Hi everyone, I'm really confused with a particular question: Homework Statement A space shuttle orbits the Earth at 6720 km from its centre. The gravitational field strength is 8.9N/kg. Calculate the shuttle's orbital period in minutes... Homework Equations g=4pi^2...
50. ### Kepler's equation of planetary motion

Homework Statement If a planet were suddenly stopped in it's orbit, supposed circular, Show that it would fall into the sun in a time which is\frac{\sqrt{2}}{8} times it's time period.Homework Equations Kepler's Third lawThe Attempt at a Solution