# Rotational & linear dynamics: why so similar?

## Main Question or Discussion Point

I'm not an advanced physics student -- I've only taken the basic year -- but I'm curious about a conceptual issue and wonder if someone could give me a satisfying explanation. There are obviously pretty tight parallels between basic linear kinematics/dynamics and the rotational equivalents -- so (F = ma) is analogous to (torque = moment of inertia * rotational acceleration); and the basic equations of rotational kinematics similarly have exact analogs in the linear kinematic equations.

So why is this? It doesn't actually seem obvious that there should be a direct rotational analog to "momentum" that functions in exactly the same way, mathematically, that momentum does in linear motion. Can anyone help me out with an explanation -- is there some deeper analogy between rotating and moving in a straight line?

Again, I realize this isn't the most sophisticated question, so thanks in advance for helping satisfy my untutored curiosity.