Talk:Angular acceleration

Physics Start‑class Mid‑importance

	Physics portal This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics articles
Start	This article has been rated as Start-class on Wikipedia's content assessment scale.
Mid	This article has been rated as Mid-importance on the project's importance scale.

A question

Can someone explain why constant and non-constant torque are treated differently? Also, the article refers to equations of motion, but the torque/acceleration equation isn't really an equation of motion. Serrano24 (talk) 17:39, 23 June 2008 (UTC)[reply]

With non-constant torques, to obtain the angular position as a function of time requires carrying out some integrals (or, equivalently, solving a differential equation). This is quite different from the constant torque (constant angular acceleration case) where we can use the angular counterparts to the equations of uniformly acclerated motion. In the non-uniform torque case you would write

$I\alpha =\tau _{net}(t)$

$I{\frac {d^{2}\theta }{dt^{2}}}=\tau _{net}(t)$

which is now a differential equation. Differential equations of this form (second time derivative of position related to some -- possibly time varying -- sum of forces/torques) are what are refered to as "equations of motion", so I'm not sure I see why you say that the torque/acceleration equation isn't an equation of motion. Would something along the lines of what is above be a good addition to the section of the article on non-constant torques? --GLeeDads (talk) 16:18, 12 November 2008 (UTC)[reply]

Vectors in definition of angular acceleration

The equation which gives angular acceleration as

$\alpha ={\frac {\mathbf {a} _{T}}{r}}$

is incorrect because it denotes $\alpha$ as a scalar but the tangential acceleration as a vector. It is probably best to drop the bold and specify that $a_{T}$ is the magnitude of the tangential acceleration. I would just make this change myself, but I'm completely new to Wikipedia and don't know the etiquette yet. -- GLeeDads (talk) 16:10, 12 November 2008 (UTC)[reply]

This isn't quite correct. Defining angular acceleration as:

$\alpha ={\frac {a_{T}}{r}}$

(using the same nomenclature as above) is better in the sense that it does not incorrectly mix vectors and scalars, but incorrect in that it defines angular acceleration as a scalar. Angular acceleration, like angular velocity is a vector quantity. It specifies both the magnitude and direction of the time rate of change of the angular velocity (also a vector quantity). As it stands, the information on this page is only correct for the case of simple two dimensional rotation. For more general three-dimensional rotation, both the torque and angular acceleration need to be treated as vector quantities. Additionally, the inertia I, needs to be treated as a tensor, not a scalar quantity. As soon as I get some more time I'll try to write up a more complete page.

Description terminology

The word Velocity has the connotation distance per unit time and therefor is not a good word to use about Angular acceleration, since Angular acceleration is about the time rate of change of the angle of direction of motion and not about distance.WFPM (talk) 12:05, 30 April 2010 (UTC)[reply]