Gravitational waves and Tidal forces

[alvarogz]

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

 

[Bread18]

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.

 

[timmdeeg]

Anybody could explain me the difference between tidal forces and gravitational waves?

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.

 

[D H]

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.

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.

 

[Mentz114]

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.

(my bold)

I presume the bolded part refers to the GWs, not the everyday tidal effects. Seems entirely correct to me.

 

[alexg]

I think he just reversed Tidal gravity with gravity waves.

 

[timmdeeg]

I think he just reversed Tidal gravity with gravity waves.

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.

 

[alexg]

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

What you are describing here is gravity waves, not tidal forces.

 

[jedishrfu]

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.

 

[Mentz114]

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

What you are describing here is gravity waves, not tidal forces.

No. He has described both.

Tidal forces are usally described as the deformation (stretching and squashing) of a bunch of freely falling test particles. This occurs in free fall towards a mass ...

Tidal effect in the Scwarzschild spacetime, for instance

... 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

gravitational waves.

 

[timmdeeg]

Thanks for clarifying, Mentz114.

 

[timmdeeg]

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.

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.