The Physics of Linerider

Part I: Introduction

http://linerider.com is a flash "game" in which the user can create tracks. A rider is then allowed to slide down these tracks. If you have not played this, I recommend you DON'T play it. It is very addicting and can consume many hours of your time (hours you would otherwise spend on Digg or surfing needlessly).

In this short report, I will analyze the physics involved in line rider. An obvious question is "why not just ask the line rider programmer?". Well, that would not be too much fun. Would it? So, there is the first reason - its fun. The second reason is to give an example of a physics project that students could do as a project.

I also tried to write this in a method that would be instructive. The analysis may seem overly detailed, but I tried to give a good background to the physics needed. If you had physics in college or high school, this could be a good review.

Disclaimer: There are likely to be some mistakes in here. I know some people may get all uptight about some of my equations. I tried to simplify things as much as possible (only using vector notation when absolutely necessary). This could lead to some equations that experts might call wrong (but they are not wrong).

UPDATE: I would just like to emphasize that the goal is this report is NOT to say that the Line Rider game is bad. It is very, very good and very entertaining. I have also talked to a famous flash programmer (who pretends he has a master's degree in physics, but he doesn't). This programmer explained that with flash, it is nearly impossible to correctly calculate things in flash and that most (if not all) of the physics is faked. So there.

Methods

The basic idea is to create a track in line rider and then analyze a movie of this track. The movies were created with CamStudio software, although there are many other alternatives (but that one is free). The movie is analyzed by look at the position of the rider in each frame. This gives x,y and time data for each frame.

Tracker

There is a great free tool for analyzing videos - Tracker Video created by Douglas Brown. This software (free) has some very useful features. One is the ability to move the coordinate axis. If you watch a line rider video, you will likely notice that most of the time the rider remains in the center of the frame with the background moving (but not always). Tracker Video allows you to deal with a situation like this. It is great for all sorts of video analysis projects (and free).

Logger Pro

Although Tracker Video has tools to analyze the data collect, I chose to use Logger Pro (but data could be analyzed in any spread sheet type program). Logger Pro is not free, but I still like it.

Analysis Questions

There are many aspects of Line Rider that could be investigated, but to get started I looked at the following:

• What is the scale of the system? (how big is the line rider)
• Is there air resistance?
• What about friction? How does that work?

Answers

If you are too lazy to look at the analysis pages, here are the answers.

• The line rider's sled is about 0.99 meters long. This makes the rider about 3.7 feet tall. I claim that the line rider is a 5 year old boy.
• There does not appear to be any air resistance in the program (but this is not conclusive)
• There is no friction on horizontal surfaces. Friction does not function as one would expect on the inclined surfaces. There is some type of mechanism that causes the line rider to lose energy.