Sun vs. moon - affects on tides.

[MarkChoo]

In class today, we calculated that the amount of gravity between the sun and the Earth is 180. This is far greater than the amount of gravity beteen the Earth and the moon.

So why does the moon affect the tides rather than the sun.

My take: the sun is much farther and has a broader pull on earth, while the moon is closer and pulls in a smaller area. idk if that's right to say or not, but the biggest difference beside force of gravity here, is distance. If this is right, are they any more reasons for the moon having such a huge role in tides?

 

[negitron]

Gravitational pull falls off as the square of the distance, but tidal force decreases with the cube. It's a differential force; the force of gravity due to the Sun's pull on the near side of the Earth is only very, very slightly less than the pull on the far side. But, the pull on the far side with respect to the Moon is significantly less than the pull on the near side.

 

[ijc]

I remember looking at the figures once and seeing that the sun and moon contribute tidal forces which are of the same order of magnitude, but that the tidal force due to the moon is somewhat stronger. This was affirmed by the results of a quick search which led me to http://geography.about.com/od/physicalgeography/a/tides.htm" :

The strength of the sun's gravity is 179 times that of the moon's but the moon is responsible for 56% of the Earth's tidal energy while the sun claims responsibility for a mere 44% (due to the moon's proximity but the sun's much larger size).