# How gravitation affects tides

I know that tide is caused by the gravitational pull of moon but what I don't know is how it affects water. I have actually these doubts.

1. Why does gravity of the moon creates tides only in water?

2. Are there other things (other than water) where tides are created on earth ( I have heard that, in some moons of Jupiter tides(of ground) can be found on the surface due to Jupiter's gravity)?

3. If we take a bowl of some length; lets say 30 cm diameter and fill it with water and keep it in a full moon night. Whether it will create tide?

4. If moons gravitational pull can cause tides in seas, then why a sailor can't feel the gravitational pull of moon?

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(1) Rather complicated, has to do with centripetal force as well as gravity. (2) Yes, but it will be only for gas giants. (3) No, see (1). 4) Since there are other, stronger unbalanced forces eclipsing it. And he's tiny. See (1).$$\text{}$$ These are slightly related, so I won't tell you to split them. It would have been better to make (1) your main question, ask (4) as a separate one, and stuff (2) and (3) into (1) as supplementaries--they're sort of trivial if (1) is already answered IMO. –  Manishearth Apr 16 '12 at 6:05
Maybe interesting in this respect is Jupiters moon Io en.wikipedia.org/wiki/Io_%28moon%29 This moon has active vulcanoes, that cannot be explained by it size. These are caused by tidal effects. Not on water, but on solid material. –  Bernhard Apr 16 '12 at 6:51

How gravity of the moon creates tides only in water?

This is wrong. Tides are created by the moon on all materials on earth that have some elasticity. The raising and falling of the ground has been measured at the beams in CERN, for example. The solid ground tides are called earth tides and their height can be 40cm.

Is any things( other than water) also create tides in earth( i heard that some moons in Jupiter has tides(of ground) on the surface due to Jupiter's gravity)?

You mean "get tides", not "create tides". It is the moon mainly and not the water that creates the tides.

There is some effect in the tides from the large planets and the sun's gravitational field. That is why tide tables are needed. The source is not one. Yes there are tides on planets that have moons and some elasticity in their composition.

If we take a bowl of some length; lets say 30 cm diameter and fill it with water and kept it in a full moon night whether it will create tides?

You should measure the bowl during the tide cycle, which is close to a 12 hour one ; the full moon or not is a secondary effect. Look at the explanation in the link. You will need accurate measurements and to consult tide tables for your particular location.

If moons gravitational pull can cause tides in seas, then why a sailor cant feel the gravitational pull of moon?

The sailor and all of us feel the vector sum of the gravitational forces impinging on us at our location. One cannot distinguish the individual components unless on does a fit to the components of known gravitational sources. We are not equipped biologically for that , so it must not offer an evolutionary advantage :) . The water is lifted and the boat is lifted with the water, no?

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Does it really mean a bowl of water lift up?? I guess, tides are formed in oceans because there's room for water to rise from the low tide region. In a bowl, every part of the water experience same pull, and hence basically because the pull is not strong enough to change the density of liquid so the level should remain same!!! –  Vineet Menon Apr 16 '12 at 9:25
@VineetMenon if you look at the link, you will see that every twelve hours or so even the ground we stand on is pulled by the moon+. Everything moves up, including the bowl of water. In addition, because water has different "elasticity" the water in the bowl will be affected differently than the table and one might be able to measure the difference with accurate enough methods. I would think interferometry to start with. Now if we are talking of tide within the bowl of water, i.e. the surface pulled more than the botom, the effect would be infinitessimally small, although there in principle. –  anna v Apr 16 '12 at 10:50
I think the most visible effect on the water in the bowl would be when water is pulled left and right. When moon is exactly above the bowl, I doubt there would be any visible effect. Except that the weight of the ball+water will be a tiny fraction smaller... –  Pygmalion Apr 16 '12 at 13:56
1. The gravitational tides generate atmospheric tides, earth tides and water tides. The water tides can be found in oceans, groundwater or rivers (about the last 2 types you can read on http://www.nature.com/srep/2014/140226/srep04193/full/srep04193.html ).
2. The moon is the principal cause of the tides on Earth; the secondary cause is the sun; other causes, especially planets in our solar system, have an almost insignificant effect. Note: due to varying density per altitude in atmosphere, the lunar tides are inefficient and they are replaced by solar tides.
3. No tide will happen in a bowl because the surface tension and the adsorbtion forces are much stronger than the variations in gravity.
4. The biological sensors can't detect the too small variations in gravity induced by gravitational tides. As previously answered, the oceanic tide will lift the sailor.
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