The moon

[bebopnskat]

Will someone tell me why the moons gravitational pull is strong enough to manipulate and lift billions of gallons of water, but is unable to lift anything else.

Please keep answer simple, I only have high school education.

[d9f1c7]

The moon is tidally locked with the earth, both bodies bulge in the middle. Gravity of the moon is not enough to cause tides in rock but is enough to cause tide in liquid water. The Earth however is strong enough and the moon's bulge is approx 7m in rock. Tidal attraction is not "lifting" in the sense that an object is lifted it is about the difference in attraction varying based on the distance from the centres of mass. Look up spagattification for an extreme example of what tidal forces are.

[Canary42]

How do you know you aren't being lifted (albeit minimally) by the moon's pull ?

[RATTER15]

I dont think that anything is being "lifted" as such,gravity prevent that but I think the pull of the moon distorts and manipulates rather than lift.

[moonraker558]

I wish it would lift my trousers up....

[Old_Geezer]

Well it is only lifted in the sense that the shape of the mass of water changes, it's not lifted off the surface of the planet and flying into space. It must be easier to encourage a molecule of water to raise slightly then a large solid object to undergo a noticeable affect.

Anyway the ocean is large and so changes are noticeable, anything else you probably think of would be small in comparison, so affects would be more difficult to see; especially since solid objects are less prone to large distortion than liquids are.

[Jonathan-Joe]

The moon does "lift" the earth's crust, http://www.scientific...?id=letters-june-2008 though by an amount so small that "flexing" may be a better term. The oceans rise much more because they are liquid.

[jomifl]

Water is more fluid than 'solid 'rock which acts like a viscous fluid on a planetary scale, so it can respond to the changing gravity field more quickly. Try putting some treacle and then some water in a cup, then tip it out, my guess is that the water will be gone before the treacle reaches the lip of the cup.

[New Judge]

As has been mentioned, “lifting” is not really the right term.

All bodies exert a “tidal effect” on each other. This effect has nothing to do with “tides” in the ocean. In fact the movement in the seas which will call tides are manifestations of the tidal effect of the moon upon the earth.

A tidal effect elongates the effected body in the direction of the body having the influence. This is apparent on solid matter to a lesser degree, but in the case of the earth the liquid seas form two “bulges” on opposite sides of the globe, in line with the moon. These form the “high tides” on the coasts and, because the earth is rotating they give the impression that they are moving from east to west, giving us two “high tides” per day. (The reason each high tide occurs about every twelve and a half hours and not twelve hours is because the moon is orbiting the earth every 28 days. Its apparent position – which dictates where the high tide occurs – thus changes daily.)

[jomifl]

The sun also produces tides, these are the twice daily tides as explained by New Judge, but these are modified by the addition and subtraction of the lunar tides which occur twice every 28 and a bit days. A further complication is the additional affect of the resonant frequencies of water bodies such as the English Channel ( a bit like when water sloshes from one end of a bathtub to the other) which has several resonant frequencies, these give rise to local effects such as the extended high tides and short low tides between Poole and Portsmouth.

[jomifl]

^effect

[New Judge]

Quite so.

The tidal effect exerted by one body on another varies directly with the mass (the greater the mass the greater the effect). But it varies inversely with the cube of the distance. The Sun is 400 times more distant from the earth as is the moon, so its tidal effect is 64 million times weaker than the moon as a result of that. But it is about 27 million times more massive than the moon. So overall the Sun’s tidal effect on the earth is a little under half (27m/64m) that of the moon. When the moon and the Sun are in alignment this increases the tidal effect as they are effectively combined. But when they are at right angles the moon’s tidal effect is diminished by that of the Sun (and vice versa).

[hiflier]

If you think that explaining the moon's effect on the seas is difficult, then give this one a try: water running out of a bath through a plughole does not go straight down but spirals down. This is due to the so-called coriolis effect, whereby each molecule of water, as it is drawn down by gravity moves ever so slightly more southward (in the northern hemisphere), and because the earth rotates this means that each molecule is accelerated eastwards because objects (including molecules of water) move faster in space the closer they are to the equator, and this acceleration causes a force on the molecule (Newtons 3rd law I think) which drags it tangentially around the plughole. Simple ain't it!

[jomifl]

It's simpler than that Hiflier, when the plug is pulled out the water starts moving towards the plug hole, but in the time it takes to get to the plug hole the earth has turned underneath the water so it is not where it was when the water started moving. The result is that the water has to turn to go down the plug hole. It actually is not detectable in a bath tub because the scale is too small relative to other enviromental factors.

[Clanad]

Actually, Gaspard Gustav de Coriolis' (1792-1843) description of this phenomena has no affect on draining water or other small scale items. It's been repeated so often, that it has become a legendary "fact".

Only large scale events, such hurricanes and typhoons are so affected due to Earth's spinning on its axis. The force exerted by the Coriolis effect is simply to weak to produce any reuslt on draining water. It becomes even less of a force near the equator, hence the large scale storms aren't observed at the equator.

Water drains as it does due to several reasons, none of which are related to M. Coriolis' described effect...

[mibn2cweus]

The side of the Earth facing the Moon is about 3 percent closer to the Moon then the side opposite the Moon and is therefore under greater gravitational influence. As the Earth rotates, this variation in the Moon's gravitation influence around the globe remains aligned with the Moon. This slight almost daily variation in the Moon's gravitational influence cause the oceans to bounce like a basketball accumulating momentum with each rotation of the Earth with respect to the Moon. This momentum is further amplified and carried forward by the rotation of the Earth producing the tides.

^ I made that up ^

The gravitation force exhibited by the Moon on one cubic metre (one tonne) of water is about (I'm guessing) 3 grammes. Multiply that by all the water in the ocean and it adds up to a huge displacement of water.

^ Yup . . . I made that up too. ^

Friday, Friday . . . Friday is my favourite day! :o)

^ Someone else made that up! ^

Happy Friday 13 to all my boffin friends out there.

[New Judge]

I once visted a place in Kenya which was said to be located on the equator.

Our host had an old kitchen sink with a plug-hole which he filled with water (the sink, not the plug-hole). He took the sink a few yards north of a line he'd drawn in the sand which he designated the equator. Then he released the water from the sink and, by means of a few floating matchsticks, demonstrated that the water flowed anti-clockwise as it went down the plug-hole.

Then he took the sink a few yards south of the equator, released to water, and showed us that the water flowed clockwise down the plug-hole.

We were conned.