x3jessy wrote:

Basically I'm taking Advanced Placement Physics in my senior year of high school.  Each chapter gets more and more confusing and we're up to chapter 11: rotation. I come in for extra help from the teacher but he seems to have given up on me. My classmates are super competitive so they refuse to give me extra help. 

I was wondering if anyone had a really easy basic way of describing these concepts to me.  I just can't seem to wrap my mind around what they're talking about.

Angular Acceleration vs. Tangential Acceleration vs. Radial Acceleration

Moment of Inertia

Angular Speed

So basically the whole application and simple definition of what these things are would be super helpful if you get the chance.

Thanks!

Of course, each of these terms is defined in every introductory physics textbook on mechanics, so it sounds like you are looking for some conceptual understanding that is absent from the clinical definitions.

Conceptually, the fundamental physics that applies to linear motion carries over to rotational motion. However, since there is a difference in the two types of motion (linear is translational motion along a line, while rotational is revolving motion around a fixed axis), some of the specific terms used when describing linear motion must be modified when describing rotational motion, to account for this difference.

So, for example:

•  position x —> angular position

•  velocity v —> angular velocity

•  speed v (= the magnitude of the vector v) —> angular speed (= the magnitude of the vector )

•  acceleration a —> angular acceleration

•  mass m ("inertia") —> moment of inertia I ("rotational inertia")

•  force f —> torque

(Looking at these last 3, can you guess what the rotational analog of Newton's Second Law is?)

Tangential Acceleration vs. Radial Acceleration: The velocity of an object that is rotating about an axis is a vector quantity that changes from moment to moment. Its magnitude—which is called "speed"—may or may not change as it rotates, but its direction certainly does change. Since its velocity is changing (even if only in direction), the object will—by definition—be accelerating. Acceleration, like velocity, is a vector quantity. Being a vector quantity that is associated with rotation, it can be resolved into two components with respect to the path it follows: a tangential component ("tangential acceleration") and a radial component ("radial acceleration").