Why does the tide come in and go out again?
● The two primary agents when it comes to the motion of the ocean are the Sun
and the Moon.
● Gravity also has a more directly observable influence on our planet. Specifically,
gravitational forces are responsible for the rise and fall of the ocean’s tides all
over the world.
● Both the Moon and the Earth are constantly moving through space. Since the
Earth spins on its axis, water is kept balanced on all sides of the planet
through centrifugal force.
● The Moon’s gravitational forces are strong enough to disrupt this balance by
accelerating the water towards the Moon. This causes the water to ‘bulge.’
● The Earth’s rotation causes a sympathetic bulge on the opposite side of the
The planet as well. The areas of the Earth where the bulging occurs experience high
tide and the others are subject to a low tide.
● The height of the tides can vary during a month, because
the Moon is not always the same distance from the Earth.
● When the Sun and Moon are aligned on the same side as the Earth, the tides
they cause which are stronger than usual since they are pulling together are
called Spring tides.
● Conversely, when the Sun and the Moon are at right angles to each other and
are pulling in opposite directions, tides are weaker and are called neap tides.