561
The Environment / Re: Could the Earth ever be completely underwater?
« on: 29/11/2018 13:20:49 »Another possible scenario is when the Moon was much closer than it is now.Interesting choice of distance. At 10x closer, it puts the moon about exactly at geosync, so there would be no tides at all. If it was just a little off, yes, there would be time to form tides at full height, but also the crust of earth would bend back and forth, heating it dramatically. Maybe the heat of that would boil away the water.
Tidal forces follow an "inverse cube" law, so when the Moon was 10x closer, tidal forces would have been 1000x stronger - imagine a +/-1km tide! That would create an incredible amount of erosion - perhaps even enough to erode mountains faster than tectonic forces could push them up?
Can you explain how that works pleaseFrom wiki on tidal force:
"The tidal force acting on an astronomical body, such as the Earth, is directly proportional to the diameter of that astronomical body and inversely proportional to the cube of the distance from another body producing a gravitational attraction, such as the Moon or the Sun.
...
Figure 3: [Graph showing a simple plot of Y=1/X2]
...
In this graph, the attractive force decreases in proportion to the square of the distance, while the gradient (slope) decreases in direct proportion to the distance. This is why the gradient at any point is inversely proportional to the cube of the distance.
The tidal force corresponds to the difference in Y between two points on the graph, with one point on the near side of the body, and the other point on the far side. The tidal force becomes larger, when the two points are either farther apart, or when they are more to the left on the graph, meaning closer to the attracting body.
For example, the Moon produces a greater tidal force on the Earth than the Sun, even though the Sun exerts a greater gravitational attraction on the Earth than the Moon, because the gradient is less. The Moon produces a greater tidal force on the Earth, than the tidal force of the Earth on the Moon. The distance is the same, but the diameter of the Earth is greater than the diameter of the Moon, resulting in a greater tidal force."
The following users thanked this post: evan_au