What causes the change in the tides?

Answer 1

the gravitational pull of the moon and its current location.
The moon. Or more accurately, the gravitational effects between the earth and the moon.
The gravitational effects of the Moon, and to a lesser extent the sun. However, The water does NOT rise because of the Moon's gravity pulling on the water... that would not explain why the water on the opposite side of the earth ALSO rises. To be more precise... It's not the gravity itself, it's the Inertial effects of orbital mechanics in a gravitationally bound orbit. Tides are caused by the fact that any orbit is based upon the center of gravity of that object, and yet objects can be large enough to extend both inside and outside the orbital path dictated by their center of mass. for example: When a long thin object, such as a rocket booster, is in an orbit long enough, without artificial stabilization, it will naturally tend to orient is long axis roughly radial to its orbit. This is because of tidal tension. The end of the rocket nearest the earth is in a lower orbit... and the further end is in a higher orbit. But both ends are orbiting at the same velocity as the rocket's center of gravity... The lower end is moving a little too slowly for that lower orbit.. and the higher end is moving a little too fast for its orbit. Thus the high end experiences negative gravity... as its angular momentum creates an inertial component accelerating inward. And the low end experience the exact opposite, an inertial component accelerating upward. The center of the rocket is constantly pulling both ends to its orbital path and velocity. Only the structure of the rocket is preventing the two ends from flying off in opposite directions. One to a higher orbit, the other to a lower orbit. In a steep enough gravitational field, these tidal forces can be strong enough to tear the booster in two... Indeed... these are the forces that prevent any large moon from remaining intact within a certain radius of both Saturn and Jupiter. The tidal stress tears them into pieces. The exact same forces apply to the Earth and moon, High tide occurs when the moon is either directly overhead, or directly on the opposite side of the earth. The water on BOTH sides of the earth, being unrestrained, rises in direct proportion to the inertial component imparted by their orbit around the Earth/Moon barycenter. It is the exact same phenomenon as with the booster. And the fact that the Moon does not have uniform mass is why its rotation is tidally locked- with its longest mass axis being radial to its orbit. Eventually, Earth will also become tidally locked as the moon bleeds our rotational energy into a higher and higher orbit. The Sun exerts a much less noticeable effect, because, relative to is orbit, the diameter of the earth represents such an small difference in orbital speeds. So there are two different sets of tidal humps in the oceans... One major, the other minor. But when the moon and the sun are on precisely opposite sides of the earth, or the same side... the solar tide is superimposed on top of the height of the lunar tide.

Answer 2

Gravity. The pull by the moon on the earths gravity causes the tides here on earth.