Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gravitational flux in solar system?

  1. Dec 22, 2005 #1
    Is it correct to say that as the Earth (or any other planet I guess) gets closer to the Sun during parts of its yearly revolution, that (at incredibly small levels) gravity on Earth gets stronger (weaker?) ?

    Basically, if a planet's orbit from one year to the next stays the same, but its distance from the sun changes throughout the year (it does, correct? ), are there extremely minute fluctuations in that planet's gravity?

  2. jcsd
  3. Dec 23, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Not really. But you can say that the tides from the sun get very slightly stronger.

    Surface gravity measured at any point on the Earth's surface with a gravimeter will vary slightly with time, due to tides and tidal effects.

    See for instance

    http://www.earthsci.unimelb.edu.au/ES304/MODULES/GRAV/NOTES/tidal.html [Broken]

    However, there should be no average change in the Earth's surface gravity due to the proximity of the sun.
    Last edited by a moderator: May 2, 2017
  4. Dec 27, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    The force of the Sun's gravity will be slightly stronger when we're closer to the Sun (we're at perihelion sometime in the first week of January). This isn't the same as saying gravity on Earth gets stronger.

    When you're on the daylight side of the Earth, the Sun's gravitational force opposes the Earth's, so the net force would be weaker. When you're on the night side of the Earth, both the the Sun's gravitational force and the Earth's would add together, making the net force stronger.

    Hence pervect's answer that the 'tides' from the Sun would be slightly stronger.
  5. Jan 15, 2006 #4
    I am having a difficult time trying to compartmentalize how the Sun, even with its incredible mass, could exert any significant gravitational pull on a planet such as Pluto considering a distance of almost 3.6 billion miles. Not to mention the other even smaller objects that are "trapped" if you will, by the Sun's gravitational pull. For those of you that have the mathamatical skills let's try this as it may help my understanding-Let's substitute Earth for Pluto at a distance of 3.6 billion miles. what would be the extent of the tidal pull on the oceans. I would be surprised to find that a calculation would yield as much as an inch. What say ye!!!
  6. Jan 15, 2006 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, since tidal forces fall of by the cube of distance and Pluto is roughly 40 time further from the Sun than the Earth, The tides would be about
    1/164000 of what they are now.
  7. Jan 21, 2006 #6
    Lets see ...you probably mean the tides would be 1/64000 what they are now on Earth.
    Right Janus?:uhh:
    Last edited: Jan 21, 2006
  8. Jan 21, 2006 #7
    Well, not really, Bob. This is a common misconception. The tidal force is NOT a result of the change in the direction of the sum of the two gravitational forces. Think about it again. If that were true it would not explain why the water pulls AWAY from earth on the 'dark' side of earth just as it bulges away on the sun lit side.
    In reality, the earth is in free fall around the sun along with everything on it. The earth surface facing the sun is slightly closer to the sun than the center of earth and so it experiences a greater force as it free falls toward the sun. The earth surface on opposite side is slightly farther from the sun than the center of earth and so it 'lags behind' the center as it free falls toward the sun.
    Thus both sides bulge.
    This (solar) tidal force is a differential force which results from the difference in DISTANCE of each surface from the sun.
    --I guess I should warn you; if I turn out to be particularly clear, you've probably misunderstood what I've said.-- Alan Greenspan
    Last edited: Jan 22, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook