Finding the derivative of the radial vector r

[zachdr1]

Homework Statement

How do you find the derivative of the radial vector r

Homework Equations

r [/B]= ru'_r + ru_r

$$<b>r = </b>\frac{dr}{dt}<b>u_r</b> + r\frac{d<b>u_r</b>}{dt}$$

can't get latex to work either

The Attempt at a Solution

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

 

[kuruman]

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

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