Posted: Oct 24, 2011 10:03 pm
jamest wrote:
I would have thought that the size of the oceans was irrelevant. The gravitational effect per unit of volume, so to speak, is the same throughout and suffices to produce the overall effect of the tides. Similarly, If humans/animals were turned into a sea of liquid mush, I would expect to see a similar tidal effect (moreso, since we are heavier than water). Again, the gravitational effect per unit of volume would be the same throughout and would suffice to produce significant tidal effects. Since this gravitational effect per unit of volume is significant enough to cause the tides, I cannot understand why it makes hardly any difference to the weight of a unit of volume.
I'm just expressing my surprise, btw. I'm obviously not saying that the effect is not very small. I believe you, but don't gettit.
The calculation is simple FFS. Newton worked out how to do this over three hundred years ago!
Gravitional force of the Sun on a person. F = G Mm/r2.
Assume a spherical person (physics joke there) weighs 60kg.
F = 6.67 x 10-11 x 2 x 1030 x 60 / (2.25 x 1022) = approx .35 Newtons.
Similarly, force of gravity due to the Earth on a 60 kg mass at earth's surface approx 590 Newtons.
So the effect of the Sun is small.
Tidal forces are a different thing again. The tides are caused by the gradient in force across a linear distance. Hence tidal forces vary by 1/r3