# Time derivatives

1. Mar 9, 2012

### Fellowroot

1. The problem statement, all variables and given/known data

My question is how do I take the time derivative of (theta dot)^2?

2. Relevant equations

3. The attempt at a solution

Is the answer just 2(theta double dot)^1 or do you use chain rule 2(theta dot)*(theta double dot)?

2. Mar 9, 2012

### nucl34rgg

Well, assuming theta is a function of time, you must use the chain rule!

3. Mar 9, 2012

### HallsofIvy

Staff Emeritus
I take that your "dot" refers to differentiation with respect to time, t,- I will use a prime since it is simpler here- and you are asking about the derivative of $(\theta')^2$.

The derivative of any $(f(t))^2$ with respect to t is $2f(t)f'(t)$, by the chain rule, so the derivative of $(\theta(t)')^2$ is $2(\theta')(\theta'')$.