Talk:Kinematics

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[edit] "motion under gravity"

Removed the section on motion under gravity; it was poorly written, did not fit in with the rest of the article, and wrong. It seemed to say that Gallileo said that objects of different masses fall at different rates, which is clearly incorrect. 129.78.64.101 (talk) 14:33, 30 April 2008 (UTC)

[edit] Sundry comments

This article contains lots of nonstandard notation. This is potentially confusing. More standard notation can be found in numerous physics texts including:

Halliday&Resnick, Johnson&Cutnell, Serway


This page contains several statements at the end about angular "position" and angular velocity that are non-general; that is, they only apply to a two dimensional or planar problem. MarcusMaximus 09:20, 25 August 2006 (UTC)


I added the section Algebraic equations to the Fundamental Equations heading. Give me your thoughts - I like that notation a bit better, it's more common, and a bit easier to understand. It may not reconcile with the vector notation used, but it is algebra. --Democritus the Minor 08:10, 6 September 2006 (UTC)

I notice that the change in the algebraic equations for linear kinematics are not notated consistently with the angular portion. I prefer describing linear kinematics using vi and vf instead of v and u because there is no obvious relationship between v and u in the equations, while the relationship between the velocities is vital in understanding the equations. Additionally, if initial and final angular displacements are used in describing angular kinematics, it seems reasonable to be consistent and use initial and final linear displacement to describe linear kinematics instead of using Δ. I believe it may be sufficient to simply notate the linear equations in both ways, which is what I have done.Tgilro01 20:59, 22 March 2007 (UTC)

Of course its confusing, its Physics! Anonymous 20:56, 14 May 2007 (UTC)

Physics is a beautiful subject which is not confusing in the least. Now as for this article it seems to be a crash course in kinematics and for that it is fine. —Preceding unsigned comment added by 117.194.225.190 (talk) 12:02, 30 March 2008 (UTC)

[edit] History and Explaination

While a purely mathematical treatment is nice, we should consider some plain language description of what each term does. We also need the history of kinematics, it's major developers, and the problems they were interested in solving.

Dhskep September 24, 2006 21:22 UTC

[edit] Relativistic kinematics?

Can anyone direct me to an article on relativistic kinematics (if one exists)? If there's no such article yet, it should probably be created either separately or as a subsection of kinematics. HEL 03:09, 5 November 2006 (UTC)

[edit] Specific notation confusion

I have long understood in Physics and Maths that difference (e.g. the difference between two speeds) is notated with a Greek 'Delta' Δ symbol.
In this article, it seems the notation is 'd' for difference. Whilst this makes sense, to people who have learnt it with the delta it is confusing.
Is this simply an Australian notation? Can we look into this some how? - Eps0n 05:24, 18 February 2007 (UTC)

Where do you see d being used for the difference? Δ is used for difference in the section "Algebraic equations." Elsewhere d is used only for the differential, as far as I can see. HEL 16:23, 18 February 2007 (UTC)
I agree, I have only found d to be used for the differential, which is its standard usage and is not the same as the difference described by delta. See [[1]]

[edit] notation

Why is u used to represent initial velocity? Is this standard notation? Jhausauer 02:14, 1 June 2007 (UTC)


v0 or vi are the standard methods of representing initial velocity.

The above comment is true however it must be added that u was formerly used for denoting initial velocity. The same applies the acceleration which can be denoted by either [i]f[/i] or by [i]a[/i] —Preceding unsigned comment added by 117.194.225.190 (talk) 12:05, 30 March 2008 (UTC)

[edit] The levels are not clearly defined and the terminology is questionable

This article seems a collage of statements taken from different chapters of a physics book, and assembled whithout a logical order, and without specifying clearly where they belong in. There are various levels of kinematics, and either they should be treated separately, starting from the simplest, or the simpler levels should be defined as special cases or the most complex level.

Level 1: Point (or point mass, or particle) motion In this context it is not correct, in my opinion, to use the expression "translational kinematics"; the word "translational" is used only for rigid body motion.

Sublevels:
  • Linear kinematics in 1-D
  • Linear kinematics in 2-D and 3-D
  • Angular kinematics in 2-D and 3-D (for instance, in 3-D, the angular position of a particle rotating about a point cannot be described by a simple angle; you need a unit vector or an angular position vector...)

Level 2: Rigid body motion Here, and only here, you define the concepts of translation and rotation (see rigid body).

Sublevels:
  • Linear kinematics in 2-D and 3-D, which describes translation (it is the same as above, but first you need to select a point fixed on the body)
  • Angular kinematics in 2-D and 3-D, which describes the rotation (and this is a complex part, with several different conventions, explained in rotation (geometry))

Paolo.dL 22:06, 28 June 2007 (UTC)

[edit] Position vector: r or s?

Please do not use the symbol s for a position vector but only the symbol r. s is used in mathmatics and physics for 's = the distance along some curve C in space as measured from some fixed point' (cited from Standard Mathematical Tables). And 'ds = the vector element of a curve (=t ds)'(same source) It is extremely confusing to use s for a position vector. In it's whole this is a confusing text, mixing different elements together with not so clear relationships with each other.78.21.233.253 (talk) 16:54, 29 November 2007 (UTC) (I am Huibc in the Dutch Wikipedia)