Vector Equation Help

1. Sep 27, 2010

Jonnyb42

I am reading a book, and I see the following mathematical statements:

[PLAIN]http://mynqa.com/Cargo/Untitled2.bmp [Broken]
and I have worked it out and it makes sense.
Then another statement comes up, regarding the radial acceleration this time:
[PLAIN]http://mynqa.com/Cargo/Untitled.bmp [Broken]
This second equation does not make sense to me, when I work it out myself, using the first equation which I had successfully worked out, I arrive at the right side but missing the term:
[PLAIN]http://mynqa.com/Cargo/term.bmp [Broken]
where does this middle term come from?

I know I am not providing much information as to what the equation is expressing, that is because what I am asking is primarily mathematical. These are vectors. OH one thing to know however, in the book they define vectors with the up-arrow/hat as soley direction, (magnitude 1) and the vectors with arrows pointing to the side as normal vectors, and corresponding letters without anything overhead is magnitude.

Thanks for any help.

Last edited by a moderator: May 4, 2017
2. Sep 27, 2010

Jonnyb42

Well I found out why I wasn't getting that extra term, is it because I was foolishly considering r12 a constant, when it is differentiable.