This app earned a 2nd place finish in Kivy App Contest 2014. Please check out the other fine apps in the contest.
This app was made utilizing the kivy library. Please refer to kivy.org for its installation. Additionally, the app requires navigationdrawer and graph from the kivy-garden in order to run. The buildozer tool can be used to build the app, or the android apk in the bin can be installed directly.
fourbar is a multitouch app simulating a four a bar linkage. This app allows one to examine the motion of any four-bar linkage that satisfies Grashof's condition. The condition simply states that if sum of the longest and shortest members of a four bar linkage are less than the sum of the other two, the smallest member can make a full rotation with respect it's neighbor. When this condition is satisfied, the app will rotate the smallest member at a constantly velocity. This leads to some interesting mechanical behaviors that are difficult to express from a book or in a lecture setting. The app is also not math heavy. Rather learning is accomplished through observation and experimentation. While the app is aimed more at engineering students, I think others will find it interesting if not peek someones interest in the physical sciences.
The app itself is themed after the green tinted graphing paper that I have used to make technical drawings. I like how you can hide most of the widgets, and it looks like you are just working on a piece of graph paper. The four-bar sits in a 2D scroll so it can be easily moved to compare the motion to the graphs or get access to the motion controls on the sidebar. Length changes are made by holding down and dragging one of the bar end points. The app works in both landscape and portrait mode. I also made use of the metrics so it should look the same for multiple devices.
Here are some screen captures running on an android device.