# Finding the derivative of the radial vector r

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1. Feb 1, 2017

### zachdr1

1. The problem statement, all variables and given/known data
How do you find the derivative of the radial vector r

2. Relevant equations
r
= ru'_r + ru_r

$$r = \frac{dr}{dt}u_r + r\frac{du_r}{dt}$$

can't get latex to work either

3. The attempt at a solution

If r is the magnitude of r, how would you find the derivative of it? Wouldn't it be constant?

Last edited: Feb 1, 2017
2. Feb 1, 2017

### kuruman

It would be constant only if the object is at rest or moving in a circle.