The Moon is most responsible for Earth’s tides. Which pulls more strongly on the Earth and its oceans?

A) Moon

B) Sun

C) Both about equally

Source: forum.understandingbasics

###### Solution. Posted on Sunday, May 10, 2015.

In order to answer this question we should use the Newton’s law of universal gravitation

F=G*M1*M2/r^2

Let’s calculate the gravitational force between the Earth and the Sun

F=6.67*10^-11*1.988*10^30*5.972*10^24/(1.5*10^11)^2 = 3.519*10^22 N

Now let’s calculate the gravitational force between the Earth and the Moon

F=6.67*10^-11*7.346*10^22*5.972*10^24/(3.7*10^8)^2 = 2.137*10^20 N

Let’s compare forces

3.519*10^22/2.137*10^20=165

Finally, the gravitational force from the Sun 165 times stronger than the gravitational force from the Moon.

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