# Lunar and solar tides [closed]

I just read the following statement in a book:

If the diameter of the earth increased by 20%, both lunar and solar tides would be weakened with lunar tides weakening more than solar tides.

What does this mean? I basically don't know about solar tides and how lunar and solar tides are related.

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## closed as unclear what you're asking by Emilio Pisanty, Dilaton, Qmechanic♦Aug 26 '13 at 20:03

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Does the book say why they would be weakened? – Emilio Pisanty Aug 24 '13 at 14:52
if the diameter of earth increases by 20%.... – Rajath Krishna R Aug 24 '13 at 15:01
$\uparrow$ Which book? – Qmechanic Aug 26 '13 at 20:03

$$F \approx \frac{G M_{Earth} M_{Moon} }{r^3} d$$
where $r$ is the distance from the centre of the Earth to the centre of the Moon, and $d$ is the diameter of the Earth. $F$ is the force stretching the Earth i.e. the difference between the forces on the near and far sides. The approximation assumes that the diameter of the Earth, $d$, is much less than the Earth Moon distance.