Why does the earth have tides? I know it has something to do with the moon but what is the point of them?

Answer 1

No point really just the effect of the Moon (and Sun's) gravity pulling the water towards them. It helps seagulls find dinner if you are desperate for a plus point.

Answer 2

I tried to have this conversation with my boyfriend (after watching Big Brother and they were debating this). You are right it is to do with the moon..........

Or is it???

Who has taken the moon away so that we know that the moon controls our tides....Nobody! I think that somebody sat there one day and said I know what... I will tell everyone that the moon controls the tides!!

If you dont like my theory here is the official one.

An often-heard explanation is that it's because the Moon's gravity field pulls the water. This can't be the full explanation since the Moon pulls the solid Earth as well and does not pull the water *relatively* to the solid Earth. Also, somewhat contra-intuitively, there's high tide twice per day, namely when the Moon is highest on the sky but also when its on it lowest point below the horizon, when intuition might suggest that the Moon should be pulling water down rather than up.

The correct answer is that the variation in the Moon's field of gravity (stronger the nearer you are to the Moon) causes the Earth to have a minimum of potential energy if it where slightly elliptic. Note that such an ellipsoid has a lower potential energy than a sphere even though the center of mass is the same. While the Oceans take the minimum-energy shape, the solid Earth is too rigid to get deformed into an ellipsoid.

Maybe it's easier to understand this way: The Earth rotates around the common center of gravity for the Earth-Moon system. This rotation produces a centrifugal force directed away from the Moon. This centrifugal force is, on average, balanced by the gravity of the Moon.

The centrifugal field is
F = r omega^2, where omega is the rotational speed of Earth in its orbit around the common center of mass, i.e. it grows linearly with r which is related to the distance from the Moon at a particular point of the Earth's surface, while the lunar gravitational force is
F = - m G /d^2, where m is the mass of the Moon, G the gravitational constant and d is the distance from a particular point on Earth's surface to the Moon. The minus sign because the direction is the opposite as that of the centrifugal force.

Now the total field affecting the ocean becomes
r omega^2 -mG/d^2
differentiating with respect to r gives
F' = omega^2+mG/(3d^3)
which is always positive so that the field in the direction away from the Moon must be stronger the further away you come from the Moon. Since the average field must be zero (the gravitational and centrifugal force must balance eah other to keep the Earth in orbit), the field must be negative (i.e. directed towards the Moon) at thee location nearest to the Moon, and positive (i.e. directed away from the Moon at locations furthest away from the Moon.

Answer 3

The moon pulls at the earth. The moon is a big enough object to exert a gravitational pull. Since land is more resistant to force than water, water responds to the moon's gravitational force with tides. On the opposite side of the earth. it is the point farthest away from the moon that is being pulled the least. That means that water will rise against the land there too.

Answer 4

The moon like all solid bodies exerts a gravitational force. This acts on everything on earth but is most visible on large bodies of water - a pull we call 'tides'. Without a moon we would have no tides, a smaller moon would mean lower tides. There is no point to them other than that - like clouds, or rain, or sunshine, there is a reason for them but no meaning.

Answer 5

What is the point of anything?

The tides are an effect of the gravitational relationship between the earth and the moon. They are not purposive, however they have various effects.
Perhaps the most obvious is that they provide a special ecological niche that is exploited by many animals, that would probably not exist if the tides weren't there.
They also affect the coastlines, wearing away, and building up the land.

Answer 6

The changing tide produced at a given location on the Earth is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of the rotation of the Earth and the local bathymetry (the underwater equivalent to topography). Though the gravitational force exerted by the Sun on the Earth is almost 200 times stronger than that exerted by the Moon, the tidal force produced by the Moon is about twice as strong as that produced by the Sun. The reason for this is that the tidal force is related not to the strength of a gravitational field, but to its gradient. The field gradient decreases with distance from the source more rapidly than does the field strength; as the Sun is about 400 times further from the Earth than is the Moon, the gradient of the Sun's field, and thus the tidal force produced by the Sun, is weaker.

Answer 7

It has to do with the life in the sea, all the nutrients and ecosystems are regulated by the tide, im not sure if we as land people would survive without the moon but i know that if we all of a sudden lost the moon, things in the ocean would die.

Answer 8

tides are due to gravity, the oceans are the biggest mass to be affected by gravity on the earth,

Answer 9

Zoe is correct. Most people think that its from the moon pulling the water, but that isn't the case as much as her answer above.

Answer 10

your right..it is the moon...its the gravity interaction between the earth and the moon that makes the tides come and go...other then that i dunno what purpose it serves..other then to wash up dead fish on the water so that i can eat them...mmmmmmmm