does anybody besides me find the following wikipedia articles confusing?(adsbygoogle = window.adsbygoogle || []).push({});

http://en.wikipedia.org/wiki/Four-acceleration

a=du/dτ

γ_{u}is the Lorentz factor for the speed (coordinate velocity) u

In an instantaneously co-moving inertial reference frame u = 0, γ_{u}= 1 and dγ_{u}/dτ = 0, i.e. in such a reference frame

A =(0,a)

Therefore, the four-acceleration is equal to the proper acceleration that a moving particle "feels" moving along a world line.

should read:

Therefore, the four-acceleration within that co-moving inertial reference frame is equal to the proper acceleration that a moving particle "feels" moving along a world line.

http://en.wikipedia.org/wiki/Proper_acceleration

The proper acceleration 3-vector, combined with a null time-component, yields the object's four-acceleration. (this is just plain wrong)

even though below that:

http://en.wikipedia.org/wiki/Proper_acceleration#Viewed_from_a_flat_spacetime_slice

it correctly states:

proper acceleration α and coordinate acceleration a are related[6] through the Lorentz factor γ by α=a*γ^3

Hence the change in proper-velocity w=dx/dτ is the integral of proper acceleration over map-time t (coordinate time)

and gives these formulas:

http://upload.wikimedia.org/math/f/3/f/f3fd7fcce9b254111e10ca5bae382511.png

you can check that the derivative of proper velocity with respect to coordinate time is a*gamma^3 by entering v[t]/sqrt[1-((v[t])^2)] into this http://calc101.com/webMathematica/derivatives.jsp#topdoit

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