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What is a covector, covariant tensor, etc?

  1. Apr 29, 2008 #1
    Sorry, but some of you may think this is a stupid question. (I'm only 16 years old.)

    I have just now gotten into the field of tensors and topology, after studying vector calculus and differential equations and I have two questions:

    a) What exactly is a covector?

    b) What is the difference between a contravariant and covariant tensor, and any mixture of the two, in a geometrical sense? (I already know the transformation equations but I find it hard to deduce a relative view of these.)

    Any help will be especially appreciated as I cannot find any source that will explain this to me. Thank you.
     
  2. jcsd
  3. Apr 29, 2008 #2

    Dick

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    I don't think words will help you much. But a vector, is, uh, a vector. It points in a direction. A covector is a thing like a gradient. They transform oppositely under coordinate transformations, they are duals. If you know the tranformation rules then you know the difference. See, I told you words wouldn't help much. The interesting thing is that the product of a vector and a covector is the rate of change along a direction which is an INVARIANT. Because the opposite transformation rules cancel out. Welcome to the Forums!
     
  4. Apr 29, 2008 #3

    Hurkyl

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    There is an analogy:
    vectors : curves :: covectors : functions
     
  5. Apr 29, 2008 #4

    TMM

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    Hey, sounds like I'm in the same exact position you are. (16 and just covering tensor notation.) I think of covariance and contravariance in terms of how scale factors work out and all that. When I first read about it I didn't gain a good intuition of them at all until I started doing lots of problems and began to notice the properties the literature talks about emerging in the math I was doing.
     
  6. Apr 30, 2008 #5
    Thanks. I have heard of tensors being something like transformations but I got confused by thinking how a transformation could be transformed by those equations. I will keep reading up on this. Thank you.
     
  7. Apr 30, 2008 #6

    HallsofIvy

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    The crucial point about tensors is that they transform "homogeneously" when you change coordinate systems. That is, the components of the tensor in coordinate system x' are just a sum of products of the components of the tensor in coordinate system x times numbers depending on the two coordinate systems. In particular, if the components of a tensor are 0 in one coordinate sytem, they are 0 in any coordinate system. If we write an equation as A= B, where A and B are tensors, that is the same as A- B= 0. If that is true in one coordinate system, it is true in any. Since physical laws are independent of human-created coordinate system, tensor equations are the natural way to write them.
     
  8. May 6, 2008 #7
    Thanks! I just figured out that I had this book that explained dyads on the last chapter but I have only read half of it. I will finish it now that I know what it is talking about.
     
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