Talk:Kinematics

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[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)

[edit] New Introduction

I think that the introduction should be rewritten to include an example of a classic dynamics problem. I don't really know how to do the equation stuff, but maybe someone could put in a problem discussing pulley attached to a pulley, one car catching up to another car, or some kind of bicycle gear ratio. This could give a more practical perspective on what the rest of the article is talking about. Also, I don't think that any discussion of when kinematics is taught is necessary. This what I think the intro should look like (rough draft, please edit!):

START OF PROPOSED INTRO

Kinematics is the branch of mechanics concerned with the motions of objects, treating only the geometric aspects of motion without being concerned with the Force causing the motion. Because the purpose of kinematics is understanding the way objects move, many problems are concerned with position, velocity, and acceleration.

A classic problem is finding the magnitude of the velocity of a roller coaster in a helical path defined as x = c*sin(kt), y = c*cos(kt), and z = h - b*t. c, b, k are constants, t is time. X, y, and z are spatial coordinates. To find the velocity, first take the derivative of each component, then find the magnitude.
The x-component of velocity is then

v_x = \frac{dx}{dt} = c*k*cos(kt)

The corresponding y-component is

v_y = \frac{dy}{dt} = -cksin(kt)

And the component of velocity in the z-direction is

v_z = \frac{dz}{dt} = -b

To find the magnitude of velocity, we take the Dot product of the velocity with itself, and then take the square root of that value.

|v| = \sqrt{v\cdot v} = \sqrt{v_x^2 + v_y^2 + v_z^2}
|v| = \sqrt{(ck)^2*cos(kt)^2 + (ck)^2*sin(kt)^2 + b^2}

Because the identity cos<super>2</super>(kt) + sin<super>2</super>(kt), we can factor simplify the expression.

|v| = \sqrt{(ck)^2 + b^2}

In this example, we found information about the motion of the roller coaster without using any information about the forces acting on the roller coaster.

END OF PROPOSED INTRO

I also made some minor changes to the article to make the writing flow a bit smoother.

Joe056 16:33, 10 September 2006 (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)

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