A Question of Physics 101

[alexy]

parallel lines is not different in the three geometries, just the number of parallel lines.

[charlieb]

Parallel - each point on line A equidistant from its counterpart on Line B - in plane (as in two dimensions) geometry. In 3-D things get a bit trickier, double helix for example - pairs of points equidistant but the "lines" aren't straight. Euclidian and Non Euclidean geometry have different sets of Theoroms and Axioms. And when you want to play in "n" dimensions Analytical Geometry is pretty handy. You can describe a closed shape that has an infinite surface are and no volume and another that has infinite volume but no surface are. The mobius strip has either no outside surface or no inside surface. Besides, we don't live on a plane but rather more or less of a sphere - and we're basically stuck operating on or above the surface. Then there's Einstein's "deformed/curved space" idea that raises all kinds of hell with plane geometry.

charlie b

[J T]

Fri, Apr 20, 2007, 10:46am (EDT-3) [e-mail] (GROVER) physics us with: The question is: If you hang two plumb bobs, say 50 feet apart are the strings parallel?

Maybe. Unless the wind is blowing.

However, you left out too many pertinent details to give an absolute answer: How long are the plumb bob strings? Are the strings the same length? What are the strings attached to? What type of knots were used? Were both strings tied with the same type of knot? Are both strings attached at the same level? Can you see both plumb bobs at the same time?

When you can provide answers to these questions, then you can receive a viable response to your original question. Unless more questions come up in the meantime that is. Next time properly research your questions, before you ask them.

JOAT Expensive tennis shoes won't cure a sore toe.

- Bazooka Joe

[Larry W]

No, they have to be approximately 12,500 miles apart for that.

[Leon]

I just had a vision of the alien guy from Mars wearing the Spartan helmet on the TV cartoon. ;~) Bugsbunny IIRC

Thanks for that one.

[Robatoy]

The weight, material and shape of the BOBs come into play in a windy model. Or not. Either way, plug in all the info, wind up the ol' 'puter out comes the answer and BOB is your uncle.

[Glen]

I was in HS when they built the Verrazano Bridge in NY. I remember one of my teachers explaining that the uprights had to be 6" out of parallel due to the curvature of the earth. I don't know if the number is accurate, but that is what I recall (after forty years or so).

Glen

[Roy Smith]

Let's do some quick math.

The towers are about 700 feet tall, and the Earth's radius is about 4000 miles. 700 feet / 4000 miles is about 1 part in 30,000.

Since arc length is proportional to radius, the tops of the towers are 1 part in 30,000 further apart from each other than their bases. The towers are about a mile (call it 5000 feet) apart, so the tops are about 5000 /

30,000, or 1/6 of a foot further apart than the t> Due to the height of the towers (690') and their distance apart (4260'), the

Not bad for back of the envelope, huh?

[efgh]

You're a star. :)

[Maxwell Lol]

String Theory

[Maxwell Lol]

Second question - How far apart are the values?

[Maxwell Lol]

Ding Ding Ding Ding. We have a winnah!

[Father Haskell]

Also, the plumb bobs contain mass, and exert gravitational attraction upon each other. That would further take the strings out of parallel.

[John]

Technically - no.

For single story building construction - close enough ;-)

John

[Father Haskell]

Or one directly over the other.

[Robatoy]

??

[Rick M]

I think we're picking fly shit out of the black pepper once again.

Plumb bobs in use are never parallel unless one is inside the other ... in which case they would be coaxial as well. In our imperfect world, they're often close enough to being parallel as not to cause us worry. That doesn't stop the pepper pickers however.

Go make some sawdust.

[Buddy Matlosz]

That depends on what your definition of the word "fan" is.

B.

[CW]

:)

[Morris Dovey]

| Since I've been enjoying the topics and discussions of this news | group, and I see that there are many posters who are quite bright, I | decided to pose a question concerning the laws of physics to | stimulate the group's curiosity. | | The question is: If you hang two plumb bobs, say 50 feet apart are | the strings parallel?

Since you make it a physics question rather than a woodworking question, the answer is that two separate strings can never be parallel.

"The proof is left as an exercise for the student." :-)

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA