Originally Posted by Zeke (Post 10522942)

Even small lakes follow the curvature of the earth. Thinking theoretically, if one had a level capable of seeing a highway built exactly level, it would rise as a tangent to the curvature of the earth. The earth curves 7.68" per mile. So a dead level highway a 1000 miles long would be 768 feet high at the far end.

Dead level Los Angeles to Las Vegas and you could just about step out of your car at the penthouse of the MGM Grand. (not quite — 230 feet vs. the total height of the MGM at 293.)

Originally Posted by herr_oberst (Post 10522596)

Will we be seeing a This Old Swartzwel channel soon?

Originally Posted by Zeke (Post 10522942)

Dead level Los Angeles to Las Vegas and you could just about step out of your car at the penthouse of the MGM Grand. (not quite — 230 feet vs. the total height of the MGM at 293.)

Originally Posted by Zeke (Post 10522942)

Even small lakes follow the curvature of the earth. Thinking theoretically, if one had a level capable of seeing a highway built exactly level, it would rise as a tangent to the curvature of the earth. The earth curves 7.68" per mile. So a dead level highway a 1000 miles long would be 768 feet high at the far end.

Dead level Los Angeles to Las Vegas and you could just about step out of your car at the penthouse of the MGM Grand. (not quite — 230 feet vs. the total height of the MGM at 293.)

Originally Posted by wdfifteen (Post 10523258)

So a perfectly accurate level could be curved.

Originally Posted by madcorgi (Post 10522400)

It's pretty important when wings are being screwed onto big airplanes. Mr. Higgins would know this better than me, so he can chime in.

When I worked on the 777 program, one of the sections I procured was the wing root area (section 44 and the keel beam, for Boeing folks), which were mated to Boeing-built wings, where tiny variations at the mating surfaces could put the wings pretty far off "even," which was a bad thing for a lot of reasons. This was the first digitally designed airplane, and there were targets outboard at some distance and at the tip that were laser measured within some really tight tolerance. I watched the first wing-to-body join happen on 001 and watched them hit the targets perfectly. Mighty impressive for parts designed and built 9000 miles apart by several different companies.

The key was that everybody measured things from common reference points, all called out from a level nominal point. Also--everybody used the same units of measure, which is another pretty important constant.

Originally Posted by wdfifteen (Post 10523258)

So a perfectly accurate level could be curved.

Originally Posted by Zeke (Post 10523709)

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.

Originally Posted by Zeke (Post 10522942)

Even small lakes follow the curvature of the earth. Thinking theoretically, if one had a level capable of seeing a highway built exactly level, it would rise as a tangent to the curvature of the earth. The earth curves 7.68" per mile. So a dead level highway a 1000 miles long would be 768 feet high at the far end.

Dead level Los Angeles to Las Vegas and you could just about step out of your car at the penthouse of the MGM Grand. (not quite — 230 feet vs. the total height of the MGM at 293.)