![]() ![]() While the Sun has a larger force on the Earth than the Moon, the Moon has a larger stretching force. ![]() The size of the Earth is a much larger fraction of the Earth-Moon distance than it is of the Earth-Sun distance. For the stretching of the Sun on the Earth we get:ĭ E / R SE = 12,700 / 1.5 × 10 8 = 8.5 × 10 -5įor the stretching of the Moon on the Earth we get: (Calculus is needed to derive the result precisely.) Let's call the Earth's diameter D E. We can make a good approximation for the strength of the tidal force by taking the gravity force we have just calculated and multiplying it by the ratio of the front-to-back distance of the Earth divided by its distance from the Sun or Moon. Tides are caused by the difference between the gravity force on one side of an object and the other side. So the gravity on the near side of a large object is larger than the gravity on the far side. So how can the Moon cause the tides on the earth? Gravity depends on the inverse square of the distance. There is no question that the Sun controls the orbit of the Earth. So the Sun's attractive force on the Earth is over a hundred times the size of the Moon's attractive force. The distances from the Earth are R SE = 1.5 × 10 8 kilometers (1 Astronomical Unit or A.U., by definition) and R ME = 3.8 × 10 5 kilometers. The masses of the Sun and Moon are M S = 2.0 × 10 30 kilograms and M M = 7.4 × 10 22 kilograms. Now we can insert the values to get the answer. Schematic of the tidal forces of the Moon on the Earth's oceans. ![]()
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