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

Gravitational waves and Tidal forces

  1. Jan 9, 2012 #1
    Anybody could explain me the difference between tidal forces and gravitational waves?
    My question emerges from the fact that gravitational waves has never been detected and also considering that tidal forces are very well understood by current physicist.


    Thanks
    AG
     
  2. jcsd
  3. Jan 9, 2012 #2
    Tidal forces are caused by the varying strength of gravity over distance, meaning an object will have differing strengths of gravity from an object. For example, the earth and the moon. The side of the earth closest to the moon will have a strong pull from the gravity of the moon then the side father away.

    Gravitational waves are ripples that propagate through spacetime as a wave. I'm not the best when it comes to this, but I think they are caused by high mass binary pairs (eg 2 orbiting neutron stars). These orbital period of these stars will slowly decrease over time, meaning they are getting closer, and losing energy. This energy is emitted as gravitational waves.
     
  4. Jan 10, 2012 #3

    timmdeeg

    User Avatar
    Gold Member

    Tidal forces are usally described as the deformation (stretching and squashing) of a bunch of freely falling test particles. This occures in free fall towards a mass and periodically in the transverse plane of a gravitational wave passing by, the plane perpendicular to the direction of the propagation of the wave. There is confidence that this tiny effect will be measured by means of laser interferometry.
     
  5. Jan 10, 2012 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Huh? We observe tidal forces every day. They are responsible for the tides, both the ocean tides and the earth tides. They are also responsible for the gravity gradient torque that act on artificial satellites.
     
  6. Jan 10, 2012 #5

    Mentz114

    User Avatar
    Gold Member

    (my bold)

    I presume the bolded part refers to the GWs, not the everyday tidal effects. Seems entirely correct to me.
     
  7. Jan 10, 2012 #6
    I think he just reversed Tidal gravity with gravity waves.
     
  8. Jan 11, 2012 #7

    timmdeeg

    User Avatar
    Gold Member

    No, he didn't.

    Once again:

    The Gravity of a mass causes tidal forces. An example are the tides, driven by the combinded gravity of moon and sun. Remember "stretching - squashing".

    Gravitational waves cause tidal forces as well, as mentioned.

    He recommends to read the resp. Wikipedia articles, for forther details.
     
  9. Jan 11, 2012 #8
    What you are describing here is gravity waves, not tidal forces.
     
  10. Jan 11, 2012 #9

    jedishrfu

    Staff: Mentor

    If you fall into a BH you will be stretched out like taffy due the gravity gradient between feet and head. This is called a tidal effect.

    Larry Niven in his sci fi book Neutron Star wrote a few stories about one where the pilot curled into a baby position to minimize the effect. Not sure if that would really work but his spaceship was indestructible built from a single molecule but that's another story.
     
  11. Jan 11, 2012 #10

    Mentz114

    User Avatar
    Gold Member

    No. He has described both.
    Tidal effect in the Scwarzschild spacetime, for instance

    gravitational waves.
     
  12. Jan 11, 2012 #11

    timmdeeg

    User Avatar
    Gold Member

    Thanks for clarifying, Mentz114.
     
  13. Jan 11, 2012 #12

    timmdeeg

    User Avatar
    Gold Member

    And you will be squashed perpendicular to the free fall direction. The two effects, stretching and squashing cancel each other, so the distortion doesn't change the volume.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Gravitational waves and Tidal forces
  1. About tidal forces (Replies: 70)

Loading...