Tuesday, December 6, 2011

Free App Today - Planet Laws - Know Your Solar System

http://itunes.apple.com/us/app/id418516576?mt=8

This app demonstrates the physics of the motion of the planets around the Sun. It is a complex topic that I have made great effort to present in the simplest possible way. Almost every page has an "Explanation" link on it, which explains how to use that page. The app is different from other apps on the same topic in that the emphasis is not on spectacular visual effects - or the current positions of stars and planets, but on getting to a solid grasp of the concepts underlying planetary motion. My hope is that it appeals to anyone of any age who considers him or her self to be a student of science, astronomy, or physics. If you are reasonably comfortable with high school level algebra, you should be able to make sense of the mathematics presented in this app.

Newton's Law of the response of a planet to the force acting on it is :

F = m * dv/dt

"dv/dt" is an expression from differential calculus. For doing a numerical simulation of the type presented in this app, the calculus reduces to algebra and the equation becomes :

F = m * delta_v / delta_t

The meanings of all these variables are explained in the app, along with a presentation of the numerical solution to these equations of motion. In the app itself, we use the text "delta_v" and "delta_t" instead of the triangular delta symbol, to make the mathematics look a lot more English like.

In addition to the above, the app presents the following features:

- Dazzling Planetary Photographs : 360 of the best close-up photographs of the planets and of the Sun, hand-picked from NASA's vast archive of planetary photographs.

- Data on Each Planet : Factoids on each of the planets.

- Descriptions and Mythology : Descriptions of the characteristics of each of the planets, along with a presentation of what each of the planet names translate into in terms of figures from Greek and Roman mythology. Also, our approach to Pluto, which is officially no longer a planet, is given in the description section for Pluto.