Rotational inertia

1. Feb 3, 2004

celect

In the terms of rotational inertia why is it hard to walk without bending your knees?

The greater the bulk of the object mass to its axis the greater its rotational inertia.
how can I relate that to walking without bending knees?

I understand that with rotational inertia an object resist
any change in its state of rotation. I just down know how to
phrase this question

2. Feb 3, 2004

Staff: Mentor

The harder something is to get spinning, the more rotational inertia it has. If you want to get something spinning, does moving it closer to the axis of rotation make it easier or harder?

Let's take an example. Say you are standing with a 10 pound dumbell in each hand. Which way makes it easier for you to get yourself spinning (around a vertical axis): (1) holding your arms straight out and the weights as far from your body as possible?, or (2) holding your arms bent, the weights as close to your body as possible? The configuration that makes it easier to turn is the one with the smaller rotational inertia. Got it?

So... what are you doing when you walk? You are rotating your leg about your hips, right? What does bending your knee do?