Well, ultimately, because for thousands of years people have been noticing that tides rise and fall, and they've also noticed that the time between one high tide and the next is pretty constant (there are small variations, but in most places it's about twelve and a half hours between, so if there was high tide at noon today, tomorrow there will be one at about 1 pm. and the day after that at 2 pm, and so on).
The rise and fall of the ocean's surface is called the tide. The tide is caused by the gravitational pull of the moon.
That would be TIDE.
Tide.
The tide
i think it is the tide
tide
no its not
tide
tide
The periodic fluctuation of the sea is called tides.
moon and sun
Tide.