Newbie component question - level measurer

wayneh

Joined Sep 9, 2010
17,496
I don't know why you are using 4000 miles since the radius of the earth is less than that.
Really? You're calling him out for using 4000 instead of 3959?

Geeesh! :rolleyes:

Oh, and I calculated the error for a building 2500 feet long is only 1.8". It's 8" for a mile but the error depends on the square of the distance.

If you can see across a 5 mile lake, the curvature error is 16 feet! I can tell from experience this is true - if you look across a lake into a harbor, it looks like all the sailboats have sunk since you can only see the tops of their masts.
 
Last edited:

#12

Joined Nov 30, 2010
18,224
Thanks. I spent over an hour looking for blueprints that were labeled in degrees of planetary angle. You just saved me from continuing that task.
 

LDC3

Joined Apr 27, 2013
924
Really? You're calling him out for using 4000 instead of 3959?

Geeesh! :rolleyes:
My point was that to have a distance of 4000 miles on the surface of the Earth, you would cover about 1/6 the circumference and the tangents at the ends of the building will meet at about 60 degrees. I guess I should have expressed myself instead of thinking that the forum was able to think for themselves. :D
 

wayneh

Joined Sep 9, 2010
17,496
Huh? You said specifically that the radius is less than 4,000 miles which is true, but the estimate is only ~1% off. Check out the links I provided if you're interested in such things.

I was amazed to learn that surveyors also have to consider lens effects due to the refraction of air. What seems so simple around the house becomes quite challenging when you scale up.
 

LDC3

Joined Apr 27, 2013
924
Huh? You said specifically that the radius is less than 4,000 miles which is true, but the estimate is only ~1% off. Check out the links I provided if you're interested in such things.
OK, I may have remembered wrong, but I knew that it was less than 4000 miles; I just thought it was between 3800 and 3900 miles (I guess I should check on the facts before I post messages). But want I wanted to point out was that 4000 miles covers a significant portion of the surface and that the floor is either curved, or water flows towards the center.
 

THE_RB

Joined Feb 11, 2008
5,438
The rule of thumb is 8 inches of drop per mile ...

The world's largest building (Boeing factory) might be a half mile long, so I have to think a 4" error had to be dealt with. I have no idea how.
It is probably floored in poured concrete, and each section would self level via gravity and vibrators, and each floor section would butt the same level as the adjoining section.

So I think it's a safe bet the Boeing factory is "bent" around the planet.
 

wayneh

Joined Sep 9, 2010
17,496
So I think it's a safe bet the Boeing factory is "bent" around the planet.
I agree. It would require extraordinary effort with novel building methods to do it "straight". And why? I don't think it would gain anything. The far walls would be off plumb.

Now I wonder about those big physics accelerators. I bet they aren't bent.
 

#12

Joined Nov 30, 2010
18,224
I agree. It would require extraordinary effort with novel building methods to do it "straight". And why? I don't think it would gain anything. The far walls would be off plumb.

Now I wonder about those big physics accelerators. I bet they aren't bent.
While I was working with self leveling lasers, a story was told to me about the Sears Tower in Chicago. They used a laser for, "straight up" and then used the rotating lasers for, "level" from the center line. IF they used a laser to pour the slab, that would imply the slab to be laser straight and have the previously mentioned "low spot" in the middle. The walls would be dead square to the slab.

IF the slab was curved with the planet, the angle of the walls would have to be a little bit off 90 degrees where they met the slab. If they used a water hose level for the slab, as the ocean is curved, so would the water levels in the hose track the curvature of the planet.

Verry interesting. I can imagine the workers attaching angled concrete mounts (for the steel beams) to the corners of the concrete slab (which is water level curved), and wondering why the designer is "compensating" for their excellent concrete work.

Ps, about the alleged 4000 mile radius of the Earth...I'm an analog guy. I don't do better than 1% accuracy :D

But seriously, I was doing the math to satisfy ME. If anybody wants the answer more accurate, they should also consider that our planet is kind of bulgy in the southern hemisphere.
 
Top