Curvature of the sea Surface

Hi, I have a Question. If I make a straight line below sea level when will the straight line emerge from underneath water. Based on the curvature of the earth. Lets say that the line starts at a seawall 10 meters beneath sea level. At how many meters from the seawall will the line emerge from under water.. Thank you. this is very important. It will help solve global warming. Thank you again. This is not a homework Question. Upkar Gill.
- Upkar Gill (age 27)
Surrey,BC,Canada

I assume that you mean that line is not only straight but also initially parallel to the sea surface. This is essentially the same problem (upside down) that the ancient Greeks solved to estimate the size of the Earth from the disappearance of ships over the horizon. 10m is so small compared to the radius of the Earth (~6,000,000m) that we can use the small-angle approximation:

d²=10m*6,400,000m, so d is about 8km.

If you're thinking of some plan to harvest tidal energy, there are a already some workable designs.

Mike W.

(published on 09/04/2013)