Speed of Moon without Sun gravity.

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Discussion Overview

The discussion revolves around the speed of the Moon relative to Earth in the hypothetical scenario where the gravitational influence of the Sun is removed. Participants explore the implications of this scenario on the Moon's orbital dynamics, calculations, and the nature of gravitational interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the speed of the Moon without the Sun's gravitational pull and suggests calculating the average distance between apogee and perigee.
  • Another participant provides a formula for the Moon's speed based on its radius and orbital period, noting that the speed differs with and without the Sun's influence.
  • Some participants argue that the effects of the Sun on the Moon's orbit are not negligible and that the average velocity would not be zero.
  • There is a proposal to treat the Earth-Moon system as a two-body problem, but this is contested by others who emphasize the complexities of gravitational interactions.
  • One participant mentions a specific speed of 3279 km/h for the Moon without the Sun's influence, which is met with skepticism and calls for calculation verification.
  • Another participant discusses the tidal effects of the Sun and how they influence the Moon's orbital period, suggesting that these effects lead to observable discrepancies in calculations.
  • Several participants express frustration with the hypothetical nature of the questions posed, indicating that without gravity, the concept of speed becomes meaningless.
  • There are references to the three-body problem and the challenges of isolating the Earth-Moon system from the Sun's gravitational effects.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of removing the Sun's gravity from the Moon's orbit. There are competing views on how to approach the calculations and the significance of the Sun's gravitational effects on the Moon's speed and orbital dynamics.

Contextual Notes

Participants note the complexity of gravitational interactions and the limitations of hypothetical scenarios. There are unresolved mathematical steps and assumptions regarding the nature of speed in the absence of gravity.

Who May Find This Useful

This discussion may be of interest to those exploring orbital mechanics, gravitational dynamics, and the implications of hypothetical scenarios in astrophysics.

  • #31
D H said:
What he said.

Hello D H,
you didn't understand me, as i said:

SpeedofLight said:
the moon makes 360 degrees around Earth with respect to stars the Earth-moon system moves 26.92952225 degrees around the sun.We can calculate ø from the period of one heliocentric revolution of the Earth-moon system (365.2421987 days):
ø = (360 degrees / 365.2421987 synodic days) x 27.32166088 synodic days = 26.92952225 degrees. So,the speed of moon without Sun gravity should be like this:
V = (2 * pi * R / T)*cos[26.92952225]
Is this CORRECT?
then you said:
D H said:
No.

Assuming no other bodies are present, Newton's law of gravity yields an equation for the period of a pair of bodies orbiting their common center of mass. You need to use that equation.

I will tell you a simple example:
The velocity vector is defined by the speed and also by the direction of motion. Objects experiencing no net force do not accelerate and, hence, move in a straight line with constant speed: they have a constant velocity. However, even an object moving in a circle at constant speed has a changing direction of motion. The rate of change of the object's velocity vector in this case is the centripetal acceleration.

The centripetal acceleration varies with the radius of the path and speed of the object, becoming larger for greater speed (at constant radius) and smaller radius (at constant speed). If an object is traveling in a circle with a varying speed, its acceleration can be divided into two components, a radial acceleration (the centripetal acceleration that changes the direction of the velocity) and a tangential acceleration that changes the magnitude of the velocity.
So, this formula V = (2 * pi * R / T)*cos[26.92952225] is right,that should find speed of moon without sun gravity from Earth-Moon System(i think the orbit of moon would be very close to circle).
The Speed of Moon Relative to Earth without the gravitational pull of the sun from Earth-Moon System is 3282.9 km/h (roughly).

Thank you.
 

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