Newton, after arriving at the expression of the gravitational force, 
, he used it to conduct studies and interpret a variety of phenomena that occur in nature, such as the tides. Many of the phenomena he studied were already known, there was just no scientific explanation for them. Newton's success in explaining these phenomena was a great triumph for the theory of Universal Gravitation.
the tides
The tide is one of the best known natural phenomena. This phenomenon occurs due to the periodic movement of the water level rising and falling, thus producing the so-called high and low tides. It was Isaac Newton who, from the expression of the gravitational force, gave the explanation for this natural phenomenon. According to the explanations of the physicist and mathematician Newton, the tides are caused by the attraction of the Sun and Moon on the waters of the sea.
The forces acting on the tides occur because the Earth is an extensive body and the gravitational field that is produced by the Sun or Moon it is not homogeneous at all points, as there are some points on Earth that are closer and others farther from these bodies. heavenly. These gravitational fields cause accelerations that act on the Earth's surface with different intensities. In this way, the masses of water that are closer to the Moon or the Sun accelerate with greater intensities than the masses of water that are farther away from these stars. It is this difference in points closer and farther from the Sun and Moon that gives rise to the tides.
By Marco Aurélio da Silva
Source: Brazil School - https://brasilescola.uol.com.br/fisica/newton-explicacao-das-mares.htm