
#1
Aug2608, 04:24 PM

P: 374

I wonder if anyone has ever heard this terminology. What is the meaning of a 3vector?




#2
Aug2608, 04:32 PM

P: 77

The number just refers to the number of dimensional components. A 2vector has components in two dimensions (X and Y) whereas a 3vector has components in three dimensions (X Y and Z).
V 



#3
Aug2608, 04:36 PM

Emeritus
Sci Advisor
PF Gold
P: 16,101

Sometimes, it refers to wedge products of vectors  i.e. a 2vector would have a planar direction and magnitude, while a 3vector would have a spatial direction and magnitude.




#4
Aug2708, 04:38 PM

P: 374

3vector, 2vector?
i knew I was not asking it right! Sorry. I actually meant 0form, 1form, 2form...
I believe they are referred to the idea of manifold, but I am not actually sure I know what a manifold is. Is it just any entity that resembles a plane if zooming at a point? That does not make sense right... any example? 



#5
Aug2808, 03:03 AM

P: 77

A manifold is a nonorthogonal coordinate system, where euclidean geometry applies at a local level. Consider the surface of the earth. At a large scale, Euclidean geometry does not apply, but if you zoom in to a relatively smaller scale, Euclid's axioms begin to apply again. One can also think of it as a patchwork, lots of small Euclidean systems joined together to form a nonEuclidean manifold.
V 



#6
Sep208, 11:58 AM

P: 374

Clear answer Varnik. So you say it is a coordinate system, which is a way to describe/ locate something in 3D space.
The spherical, rectangular, cylindrical coord systems can then also be a called manifolds if they are locally very similar to a flat plane (2D cartesian system?). the patches you talk about are 2D (x and y). Can the manifold be locally similar to a 3D Cartesian system? Any example. Can manifolds be though as something else too, besides coord. systems? Here a reply I found on DR. Math website. Hope it helps(me and others): "Take a part of a plane (which is twodimensional, right?). Cut out a part. Now, this plane is actually made of rubber. So you can pull it and stretch it and squish it and curve it and do most anything to it. (but you pop it if you make a sharp point or edge, so you can't do that  a type of mathematician called a 'topologist' loves to do this.) Now, you can twist it around some and get part of a sphere, right? if you put this sphere in threedimensional space, that means you have a 2manifold in 3space. 3space just means three dimensional space. (mathematicians like to sound cool by saying 3space.) Similarly, take a long line made of rubber (very thin rubber!). If you stretch it and curl it and put it in a plane, we call it a 1manifold in 2space. If we put it in a threedimensional space, we call it a 1manifold in 3space. Now for the really mindboggling part. Take a portion of three space (your room, for example), and twist it around and stretch it. Put it in fourdimensional space. That's what's called a 3manifold in 4space. There's no real way to picture this, which is why mathematicians tend to rely on equations, not just on pictures!" It seems that ANYTHING that has is described by ndimensions(n degrees of freedom) can be a nmanifold. It could be an object, a field, etccc. Varnick, Do you agree or am I completely off? Thanks! 



#7
Sep208, 12:42 PM

P: 77

You seem to have the idea, I cannot give an easy example of a 3manifold, although spacetime is an obvious 4manifold, it is hard to picture.
V 


Register to reply 
Related Discussions  
Vector calculus. Divergent vector field.  Calculus & Beyond Homework  3  
Deriving Vector and position vectors from Force vector  Introductory Physics Homework  3  
calculate vector with known magnitude along the direciton given by another vector  General Math  3  
I thought w(f) where w=dual vector f=vector is Reals?  Differential Geometry  1  
tagent vector and vector field difference  Differential Geometry  6 