Thread: Sensing tidal forces in a swimming pool. Possible or no?

So you have an indoor pool, still air, no geological activity to speak of, is it possible to detect tides in it, say with a couple of floats on opposite sides of the pool, maybe 4 sensors, one in each corner, and a reflector of each one that can measure a few microns of height difference between each one, average the readings taken, say once every ten minutes or so and see some difference due to tidal forces of sun and/or moon?

I doubt you'd be able to measure it. Most of the tide we observe is due to the differential lifting of the planet surface, and the waters adjustment away from that lifting because water is more viscous and able to respond more rapidly than the molten fluid under the earth's surface. Across the size of a pool, the effect would be much less than a micron of lifting.

Ray

Don't you mean LESS viscous? Isn't part of the vertical movement of water caused directly by the moon? I am no expert on tides so I would like to know.

It is an interesting question. If it is possible it would be right at the limit of detectability. I suspect that even with the absence of obvious seismic distrubances there would still be enough 'noise' from low level geological movement and human activity.
I agree with you that a) the watere is definitely less viscous and b) the water is also directly effected by the gravitational attraction.

My limited understanding of tidal activity is that it's caused mainly by effects of gravity, i.e. various locations within a huge body of water (ocean) are differently affected by the moon's gravity, leading to tides. If that's really how it works, your swimming pool better be darn large to get a measurable effect above "noise" level (the size of your pool needs to be a significant fraction of the distance between Moon and Earth). Just think of this: How much of a tidal variation do you see on relatively small bodies of water, such as small lakes and ponds?

I would say not much tidal activity in a dam or lake for sure, but it would be a darn sight easier to measure than a swimming pool for sure! I wonder about a water pipe suspended and 90 degree upwards facing bends at both ends with the suspension as isolated from seismic activity as you can get with a reasonable effort and windows for a laser to see the levels at both ends.
One thing I can see, if a person or a truck or some other mass gets near after it is calibrated, the gravitational attraction could throw off measurements. The pipe would be very well sealed of course and filled as much as possible and would have to have pressure monitors at each end, pressure relief I would assume. If one end got hotter than the other, it would simulate the effects of tides so would have to be taken into account. I imagine it would have to be closed too so wind would not make a differential change so any pressure bleed would have to be carefully monitored. I bet it could be done though. The longer the pipe, the stronger the signal.

Originally Posted by sonhouse

Don't you mean LESS viscous?

Yes my mistake. Water is certainly less viscous. (more coffee)

Isn't part of the vertical movement of water caused directly by the moon? I am no expert on tides so I would like to know.

Earth's mantle, and outer core, and oceans all respond to tidal forcing influenced by both the moon and sun. The tides we observe are the effects of the water relative to the tidal effects of that mantle and outer core, not the absolute distance from the center of the planet. In other words the earths surface is a bit higher during "low tides," because of differences in viscosity and response to the tidal effects.

Tidal effect averages only about 2 feet. Higher tides are the result of local effects such as water being channeled etc.

Ray