# Wikipedia articles

1. Sep 25, 2008

### granpa

does anybody besides me find the following wikipedia articles confusing?

http://en.wikipedia.org/wiki/Four-acceleration
a=du/dτ
γu is the Lorentz factor for the speed (coordinate velocity) u
In an instantaneously co-moving inertial reference frame u = 0, γu = 1 and dγu/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.

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:

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

Last edited: Sep 25, 2008
2. Sep 25, 2008

### granpa

3. Sep 25, 2008

### granpa

I have edited the 2 wikipedia articles in question. I would very much appreciate it if someone would double check my work.