Quote:
Originally Posted by wdfifteen
So a perfectly accurate level could be curved.
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Absolutely. If you could build a perfectly flat pool table as big as a football field, the balls reaching the ends would have a tendency to slow down more than ones moving towards the center. Thinking in the extreme, balls at the end of the table would be pulled by gravity to roll towards the center. That would have to be on a theoretical table with no resistance, e.g., no felt.
A correct pool table that size would have a crown, but it would be minuscule. I see no practical reason to take in account of the earth's curvature unless launching satellites. I was just being silly about a "flat lake."
But it's true. Being as how Lake Tahoe is at a little over 21 miles in length, if you could get your eyes right at the water's surface you wouldn't see the first few inches of the shore at water's edge. It would be roughly 6+ feet at each end that you couldn't see if you were dead center.