The diagram below shows four positions of the moon. which position produces the highest possible tides?

It is position when Moon is between Earth and Sun. In this case gravitational forces of both Moon and Sun pull water in same direction and magnitude of gravitational force is greatest. When Moon and Sun are on opposite sides of Earth gravitational force pulls water in two opposite directions and magnitude of gravitational force is smallest and tide is lower. When Moon is in position that is shown as above or below Earth than magnitude of gravitational force is between those two already mentioned.

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