## Unit 27

Unit 27 is about rotating bodies and angular momentum.
I keep getting confused.
The maths is simple enough – it’s the remembering what is what that’s the confusing bit for my decaying brain.

In particular, I keep confusing angular momentum with angular velocity.

Angular velocity is intuitively easy to visualise. Angular momentum seems less so – probably because I haven’t found a nice one-line nutshell that nicely describes it.

So, angular speed, angular velocity, position vectors and their derivatives, the torque law for “n-particle” systems, moments of inertia, cross products, Newton’s Third Law, circular motion, simple trigonometry, and lots of other things we’ve met so far on the course have all landed in Unit 27 for one gigantic party.

I’m just finishing section two now, with section 3 (angular momentum/moments of inertia/parallel axes theorem/kinetic energy of a rotating rigid body) and section 4 (torque law relative to the centre of mass/decomposition theorem/rolling objects) to come between tomorrow evening and Saturday afternoon.

The assignment question is massive – in word length, number of sub-questions and overall marks toward the final TMA.

I’m somewhat scared.

### 3 responses

1. Chris Finlay

Stick with trying to understand angular momentum, it plays a very important part in quantum mechanics.

September 7, 2011 at 9:19 PM

2. I’m on it, mate 🙂

September 8, 2011 at 6:04 PM

3. Getting there – chapter 3 was pretty much ok tonight. There are only so many finite variants of these questions that can be asked, given we have to have some initial information/conditions. I’m just metaphorically winching an OompaLoompa up and down a well-shaft at the moment. 🙂

September 8, 2011 at 9:51 PM