Anonymous asked in Science & MathematicsAstronomy & Space · 1 decade ago

Why does the MOON affect TIDES if it's always at the same distance from Earth?

11 Answers

  • Troasa
    Lv 7
    1 decade ago
    Best Answer

    Because the Earth is spinning around once every 24 hours. This causes the Moon to pull on different parts of the Earth as the Earth turns. Thus two high tides and two low tides per day.

    Source(s): The Moon's 'orbit' around Earth is elliptical but that's another story.
  • 1 decade ago

    the moon affects tides not by its distance from the earth but by merely existing near to the earth in relative terms. The fact that it is so close means that its gravity affects the earth and they both tend to attract towards each other, water being fluidic can move easily and bulges towards the moon, this is always in the direction of the moon. since the earth spins faster than the moon rotates around it it causes the effect of a tide. The same is also true of the gravity of the sun which is farther but is also much bigger and therfore has more gravity. These 2 forces pulling the water in thier directions can some times reinforce each other or interfere with each other. If the sun and moon are on the same or opposite sides othe earth the gravity of the moon and sun reinforce to pull the water even more causing a high tide, if the moon is at right angles to the sun the gravitational pull of each is working against each other thus causing a low tide.

    Source(s): the source of this info is my memory as a school kid
  • nick s
    Lv 6
    1 decade ago

    It orbits the Earth, which means that when it is over America, it is just about 7900 miles (about 13,000 kms) further away from the lands on the opposite side of Earth (India, for instance), and vice versa. That causes a gravitational imbalance.

    The fact is that when you say it is always the same distance from Earth, that is just an approximation.

    It does not, as many people suppose, just draw out the ocean nearest to it – the high tide also happens on the opposite side of the earth, but it is less extreme because it is further away.

    The sun also confuses the tidal effect, as it has just about half the moon’s effect, so the tidal effect is altered by where the sun is in respect to where the moon is.

    Source(s): Science writer
  • 1 decade ago

    The point is that the moon pull more on the side of the earth pointing towards it, and less on the side pointing away from it.

    So the water (oceans) bulge out on both the side poitning towards the moon and on the other side.

    Meanwhile, the earth turns. The moon only moves a little in the course of a day, but the earth spins thru one rotation.

    So the point on earth currently facing the moon will be pointing perpendicular to the direction to the moon in 6hrs.

    and so there's a low tide, then 6 hrs later that pint on earth is pointing directly away from the moon, so is back in a bulge and there's a high tide - and so on

    Source(s): Me - I teach this stuff
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  • 1 decade ago

    It's because of the constant distance you get constant tides because the gravity remains constant*.

    Spread some iron filings across a surface, e.g. card.

    Now slowly run a magnet the length of it underneath.

    You'll notice only the filings directly above the magnet stand up.

    The moon's gravity works he same way, dragging the water directly underneath it up. Because the Earth spins, the force acts on successive bits of water as they pass underneath. This appears to drag a bulge of water across the Earth. In the deep ocean you don't notice anything. (On land, where the layer of water is thin, you also don't notice anything.)

    When that waer bulge comes into shallower water, the sea level rises - that's the tide coming in. As the moon moves away again, the sea return to normal and even gets pulled out to fill the gap left as that bulge moves on..

    The constant distance and speed of rotation is what makes tides so predictable in timing and height.

    *If you're a real whizz, you'll know the moon is slowly drifting away from Earth, so the tides will be becoming weaker - you're hardly likely to notice it though in your lifetime!

    Source(s): Ex science teacher
  • 1 decade ago

    At the surface of the earth, the earth's force of gravitational attraction acts in a direction inward toward its center of mass, and thus holds the ocean water confined to this surface. However, the gravitational forces of the moon and sun also act externally upon the earth's ocean waters. These external forces are exerted as tide-producing, or so-called "tractive" forces. Their effects are superimposed upon the earth's gravitational force and act to draw the ocean waters to positions on the earth's surface directly beneath these respective celestial bodies (i.e., towards the "sublunar" and "subsolar" points).

    High tides are produced in the ocean waters by the "heaping" action resulting from the horizontal flow of water toward two regions of the earth representing positions of maximum attraction of combined lunar and solar gravitational forces. Low tides are created by a compensating maximum withdrawal of water from regions around the earth midway between these two humps. The alternation of high and low tides is caused by the daily (or diurnal) rotation of the earth with respect to these two tidal humps and two tidal depressions. The changing arrival time of any two successive high or low tides at any one location is the result of numerous factors.

  • 1 decade ago

    The center of the moon is not really a constant distance from the earth (but that is irrelevant here); however, note that the earth is a rather large object and that there is part of the earth that is a good 6370 km closer to the moon than the center of the planet is, and a point that is 6370 km further from the center.

  • 1 decade ago

    primarily becarse tho origin of the gravitiional pull is constantly moving and pulling on different parts of the earth's surface.

    plus, if im not mistaken the moon is in an elliptical orbit, so its not always at the same distance from the earth.


  • Eddie
    Lv 4
    1 decade ago

    the distance is always about the same, yes, but the direction of the moon changes. it moves from in beween the earth and the moon, behind earth in its orbit, beyond the earth from the sun, and ahead of the earth in its orbit. This change in directions causes the tides, not the distance.

  • Anonymous
    1 decade ago

    because it always has a gravitational pull on the ocean: two high tides a day because earth rotates

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