Deriving an equation vs memorizing a formula

[cdotter]

Hi, I'm having a bit of trouble in my second semester of physics. We're covering magnetism right now. I can understand a derivation put before me of, for example, the torque due a current passing through a wire loop. However, I could never recreate this or reach a similar conclusion on my own. I have to memorize equations in order to solve any physics problems.

I know it's a waste of time to re-derive everything on an exam but my point is that I couldn't re-derive if even if I wanted do. Somehow I can understand the derivation but I can't do it on my own.

Am I a deficient physics student because I can't do this? Or is it common among us and something that comes with intense practice and experience?

 

[PhanthomJay]

It's common to me. For example, the kinematic motion equations with constant acceleration: ..once you see, and understand, the calculus associated with the equations, you memorize them...no sense deriving them time and time again, and after awhile the equations are so imbedded in your brain so that you can recite them while sleeping. Same in engineering, I used to know how to derive the equation for Euler Buckling using differential calculus, which was important to know as to understand the principles behind the equation's solution...but now, although i know the formula by heart, I'd be hard pressed to derive it again.

 

[cdotter]

It's good to hear that I'm not alone. Anyone else?

 

[PhanthomJay]

You may not hear from anyone else since helpers often ignore a problem that is already being responded to. But I want to point out that while you don't have to derive the equation every time, that does not imply you should memorize every equation. Just memorize the basic ones, but then they have to be applied in a given problem on a case by case basis.