VPython

VPython is a Python graphics module used for modeling objects in 3-dimensional space. In the field of physics, this is especially useful for calculating and modeling complex relationships between objects and their properties.

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

VPython modeling the magnetic force on a moving particle

Installation

VPython is compatible with Windows, OSX, and Linux. While there is an older VPython version available that supports Python 3, the Georgia Tech physics courses use Python 2 syntax so it is recommended to install the latest version of VPython as outlined below.

Windows

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

VPython running in Windows 7

1. Install Python-2.7.

2. Download and install VPython from Sourceforge.

To troubleshoot any installation issues, look at the extensive VPython Windows installation guide.

OSX

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

VPython running in OSX 10.10

1. Install Python-2.7. This is required as the version of Python that Apple provides is not compatible.

2. Download and install the VPython package from Sourceforge.

To troubleshoot installation issues, see the extensive VPython Mac installation guide.

GNU/Linux

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

VPython running in Ubuntu 15.04+

Some Linux distributions include VPython in their repositories. For example, to install VPython in Ubuntu 15.04:

sudo apt-get install python-visual

If your Linux distribution's repository does not have the latest version of VPython, you can run the Windows version using Wine. The VPython Linux installation guide contains detailed instructions.

Getting started with VPython

The easiest way to use VPython is with VIDLE. VIDLE is a development environment and is the most useful for editing and running code. To start, open the VIDLE application (it may be called something like VIDLE-Py2.7). A blank file should open. Type the following two lines in:

from __future__ import division

from visual import *

The first line tells Python to not use integer division, which would result in 1/3 returning the floor 0 instead of 0.3333333333333333. The second line tells Python to import everything from the visual (VPython) library for you to use.

After these two lines, you can create objects, assign variables, do calculations, and much more. You can also run VPython from the command line, although it may require additional setup so Python can locate the visual module.

Glowscript

Another useful method of using Vpython can be found at http://www.glowscript.org/. At this website, a user can make an account and have a script up and running within minutes on a web browser without having to deal with downloading any software or worrying about compatibility. Only downside is that it can be tricky to save the code for submitting to Webassign.

Creating VPython Objects

When you create objects, it is often useful to assign them to variables so you can reference them later to either get or set values describing for example the position and size of the object.

Sphere

particle = sphere(pos=(0,0,0), radius=4, color=color.blue)

This creates a blue sphere centered at the origin <0,0,0> with radius 4.

Arrow

arrowToOrigin = arrow(pos=(0,2,0), axis=(0,8,0), color=color.green)

This creates a green arrow pointing from <0,2,0> to <0,10,0>. Note that axis is always relative to the start of the arrow, not the origin <0,0,0>.

Cylinder

wire = cylinder(pos=(0,0,0), axis=(20,0,0), radius=1, color=color.yellow)

This creates a yellow cylinder starting at the origin <0,0,0> and extending to <20,0,0> with radius 1.

Helix

spring = helix(pos=(0,0,0), axis=(10,0,0), radius=0.75, color=color.cyan)

Creates a helix of color cyan at the origin and goes to <10,0,0> with a radius of 0.75.

Pyramid

shape = pyramid(pos=(8,4,0), size=(20,4,10), color=color.red)

Creates a pyramid of size <20,4,10> starting at <8,4,0>

Object Positioning

It is very important to note that the position values for arrow, cylinder, helix, and pyramid corresponds to one end of the object, however for a box, sphere, or ring it corresponds to the center of the object.

Example

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

Result of example code

from __future__ import division
from visual import *

particle = sphere(pos=(0,0,0), radius=4, color=color.blue)
arrowToOrigin = arrow(pos=(0,2,0), axis=(0,8,0), color=color.green)
wire = cylinder(pos=(0,0,0), axis=(20,0,0), radius=1, color=color.yellow)

Updating objects If you assign an object to a variable (such as particle or arrowToOrigin above) you can adjust its parameters such as its location. For the above sphere, you can change its location to <-5,-5,0> with:

particle.pos=(-5,-5,0)

To change the axis of the above arrow to point to <-10,5,0>, use:

arrowToOrigin.axis=(-10,5,0)

To change the radius of the above cylinder to 3, use:

wire.radius=3

Example

Error creating thumbnail: sh: /usr/bin/convert: No such file or directory Error code: 127

Result of example code

from __future__ import division
from visual import *

particle = sphere(pos=(0,0,0), radius=4, color=color.blue)
arrowToOrigin = arrow(pos=(0,2,0), axis=(0,8,0), color=color.green)
wire = cylinder(pos=(0,0,0), axis=(20,0,0), radius=1, color=color.yellow)

particle.pos=(-5,-5,0)
arrowToOrigin.axis=(-10,5,0)
wire.radius=3

Useful built-in functions

VPython includes various functions that can make your calculations much easier. The following functions simplify mathematical operations on vectors and will come in handy very often.

Cross-multiply two vectors

cross(vectorA, vectorB)

Magnitude of a vector

mag(vector)

Square of the Magnitude of a vector

mag2(vector)

Unit vector of a vector

norm(vector)

Square Root

sqrt(value)

Absolute Value

abs(value)

VPython Operators

Mathematical Operators

1) # comment out a line

2) + - * / addition, subtraction, multiplication, division

3) ** exponential

4) % modulus or remainder

Logical Operators

1) == outputs true if the compared values are the same

2) != outputs true if the compared values are not the same

3) > or < outputs true if the compared values are greater or less than the other

4) >= or <= Same as above but outputs true if greater or less than or equal to the compared value

Connectedness

I am very interested in programming. I have used Python for years, so translating Physics problems into VPython code is a great way to cement the fundamental ideas in my mind.

VPython is a great tool to bridge the worlds of Computer Science and Physics. Many of the calculations required to model a physical object would be tedious if done by hand. Yet with often a few lines of code, this work can be reduced to almost nothing.

NASA has published VPython models. However, VPython is still primarily used in an educational context.

History

VPython was originally released in 2000 by David Scherer after he took an introductory physics class at Carnegie Mellon University. At the time, the school used the cT programming language for 2D modeling, and David saw the need for something better. Working with several people including professors Ruth Chabay and Bruce Sherwood, he developed a Python module called Visual. Visual Python or VPython featured 3D modeling, as well as an easier-to-understand object-oriented syntax. Beginning in 2002, the National Science Foundation had awarded $292,286.00 as of December 2015 for the further development of this tool. VPython is released under an Open Source license, and development continues today.

See also

If you have never used Python, the VPython Basics wiki page has information for getting started with Python programming.

Further reading

Aiken, John M (2013). Transforming High School Physics With Modeling And Computation. Georgia State University.

External links

You Should Be Coding in Your Physics Course

VPython Wiki Site

VPython user group

References

This section contains the the references you used while writing this page

The cT Programming Language

VPython - Python Wiki

VPython NSF Award