Least Action (Gravity/Free)
written by Todd Timberlake
The EJS Least Action (Gravity/Free) model illustrates the principle of least action for the one dimensional motion of a free particle or a particle subject to a constant gravitational force. The simulation displays height versus time, with the path broken into equally spaced time intervals. The user can set the initial and final heights, as well as the number of time intervals to be used. The user can then adjust the intermediate heights in order to minimize the action along the path, or else allow the computer to implement an algorithm for finding the path of least action. Both the action of the current path and the least action so far observed with the current parameters are displayed.
The simulation can also display average values for velocity, change in velocity, acceleration, kinetic energy, potential energy, the Lagrangian function, and total mechanical energy for each segment of the path. This helps to illustrate that the path of least action is also a path of constant acceleration (zero if there is no gravity) and constant total energy.
The algorithm minimizes the action by examining three consecutive points on the path. The outer two points are held fixed and basic calculus can be used to determine the value for the middle height that minimizes the action for this segment of the path. This procedure is repeated for each segment of three points on the path, moving left to right. If this entire process is repeated over and over the path will gradually approach the path of global least action. This approach, and the entire EJS Least Action (Gravity/Free) model, was inspired by the Principle of Least Action Interactive page by Edwin Taylor and Slavomir Tuleja.
Please note that this resource requires at least version 1.5 of Java (JRE).
1 supplemental document is available
Principle of Least Action Tutorial
This is a tutorial exercise that helps students understand the Principle of Least Action as applied to a particle moving vertically under a constant gravitational force. Students use basic calculus to derive the condition for minimizing the action along a segment of …
download 148kb .pdf
download 9kb .tex
Published: September 5, 2012
Rights: This activity handout is released under the Creative Commons BY-NC-SA 3.0 license.
1 source code document is available
The source code zip archive contains an XML representation of the EJS Least Action (Gravity/Free) Model. Unzip this archive in your EJS workspace to compile and run this model using EJS.
download 39kb .zip
Published: September 3, 2012
Rights: This material is released under the GNU General Public License Version 3.
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Least Action (Gravity/Free):
Is Based On Easy Java Simulations Modeling and Authoring Tool
The Easy Java Simulations Modeling and Authoring Tool is needed to explore the computational model used in the Least Action (Gravity/Free).relation by Wolfgang Christian
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