# Physics - Kinematics - Position

## Prerequisites

If you are not familiar with this subject you may like to look at the following pages first:

## Position Vector

We need a coordinate system to represent the position of an object. I have explained Cartesian and Polar coordinate systems here. The maths here is much easier if we use Cartesian co-ordinates, for 3 dimensions the position of any point (P) can be represented by 3 real (floating point or double floating point) numbers. This is usually represented as a vector of dimension 3:

 Px Py Pz

where the 3 numbers represent the position in each of the, usually perpendicular, directions in an arbitrary reference frame. These Cartesian coordinates are usually called x (left & right), y (up and down), z (back and forward). On this site we are using a right handed coordinate system as described here.

## Representing position in program

Position in 3D space can be held in a 3D vector (see class sfvec3f). For an example of how this might be used in a scenegraph node, see here.

## Position of particle on solid object

If we have a particle of a solid object and we want to measure its position, then:

p = cm + r

 where: other definitions symbol description type units cm position of centre of mass of object vector m r position of particle relative to object vector m p position of particle in absolute coordinates vector m

Where I can, I have put links to Amazon for books that are relevant to the subject, click on the appropriate country flag to get more details of the book or to buy it from them.

Engineering Mechanics - Includes Statics book and dynamics book below..

Engineering Mechanics Vol 2: Dynamics - Gives theory for rigid dynamics, aims to allow prediction of effects of force and motion. Includes rotating frame of reference. Lots of colour diagrams, I guess its college / University level.

Commercial Software Shop

Where I can, I have put links to Amazon for commercial software, not directly related to the software project, but related to the subject being discussed, click on the appropriate country flag to get more details of the software or to buy it from them.

 Dark Basic Professional Edition - It is better to get this professional edition This is a version of basic designed for building games, for example to rotate a cube you might do the following: make object cube 1,100 for x=1 to 360 rotate object 1,x,x,0 next x Game Programming with Darkbasic - book for above software

This site may have errors. Don't use for critical systems.