Euler's method is a numerical tool for approximating values for solutions of differential equations. It is handful since most of the differential equations are hard to solve. It is applied in a way of using the slope of the tangent line (derivative) and incrementing the x value to get the approximation of y.
These slides discuss the integration of euler's method in video game simulations. http://www.cs.cmu.edu/~jkh/video_games/jkh_simulation.pdf
Unstable it is because that all of these are only in the idealized case.
I would like to know more about why the Euler's method is considered unstable, is it due to friction or the materials of the object as it interacts with air?