# Q & A: To Be of Second Order

Q:
HI! IM DOING AN ENGINNERING DEGREE AND NEED AN ANSWER, MUCH APPRECIATED WHAT IS SECOND ORDER? THIS IS RESPECT TO CONTROL ENGINEERING
- DANIEL EUSTACE (age 18)
ALTON COLLEGE, ENGLAND
A:
Daniel -

The phrase 'second order' actually has a number of different meanings, even with respect to just control engineering. Most of these meanings have to do with math...

For example, in your high school algebra class, you probably learned about 'second order polynomials.' These are equations like x^2 + 7x + 9, or 6x^2 - 3x + 4. The reason that these equations are called second order is because the highest power of x in the equation is x^2. If you had a term with x^3, then it would be third order instead.

Another example is one that you'll probably see in your differential equations class. 'Second order derivative' is just another way of saying 'second derivative'. And in a 'second order differential equation', the order of the highest derivative in the equation is 2. That is, you'll have a second derivative in there someplace and maybe even a single derivative, but no third or forth (or higher) derivatives.

-Tamara

(published on 10/22/2007)