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## Main Question or Discussion Point

Can anyone explain to me what is contravariant and covariant? I just know that they are tensors with specific transformation properties (from website of MathWorld), i also know that the relation between two is the -ve sign.

Then dose it mean that:

given a 4-velocity of a particle is the vector

u' = dx^i/ds then how about the covariant of u'?

furthermore

given u' = { 1/sqrt (1-V^2/C^2) , v/c sqrt (1-V^2/ C^2) , then I wnat to ask am I right that the covaritant of u is { -1/sqrt (1-V^2/C^2) , -v/c sqrt (1-V^2/ C^2)?

if yes i can't get the relation u'u_' =1 (u_' indicate a subscripts)

yukyuk

Then dose it mean that:

given a 4-velocity of a particle is the vector

u' = dx^i/ds then how about the covariant of u'?

furthermore

given u' = { 1/sqrt (1-V^2/C^2) , v/c sqrt (1-V^2/ C^2) , then I wnat to ask am I right that the covaritant of u is { -1/sqrt (1-V^2/C^2) , -v/c sqrt (1-V^2/ C^2)?

if yes i can't get the relation u'u_' =1 (u_' indicate a subscripts)

yukyuk