[Via Diggy Games]

Welcome to Magic Pen. This fascinating little game displays a delightful plethora of physics principles in action. The object of Magic Pen -- as in some similar games, like Crayon Physics Deluxe -- is to roll a ball into a goal. The catch is that you can't touch the ball directly: you can only interact with it by drawing shapes with the mouse. These shapes then interact with the ball, obeying basic principles of physics. For example, draw a rock. The rock then falls due to gravity, collides with the ball, and pushes it towards the goal, which is marked by a flag.

It's impressive how many different physics concepts are embedded into the software. It's not just that objects are affected by gravitational acceleration, which is something pretty commonly seen in computer games and simulations, but they also display a variety of more complex real-world physical behaviors within the simple third-grade-art-project-like environment.

Let's highlight some of the major physics principles incorporated into the game:

• Objects released above the ground accelerate due to the effect of a constant gravitational force. Objects projected off of a ledge move in a parabolic trajectory under the influence of gravity.
• When objects collide they exert equal and opposite forces on each other, in accordance with Newton's Third Law. During the collisions, they accelerate according to Newton's Second Law. They also display conservation of momentum: the total momentum of the colliding objects is the same before and after impact. After a collision, objects continue with a constant velocity, adhering to Newton's First Law of Motion.
• Perhaps the most intriguing phenomenon is the way the game demonstrates rotational dynamics. Elongated objects that are subject to a net torque react with physically accurate angular accelerations. They even oscillate around a balancing point when disturbed, if the center of gravity remains above the base of the object.

On top of all that, the music creates a pleasant atmosphere that makes Magic Pen an addicting yet Zen-like computer physics experience worth looking into. Try it for yourself!

Adam Weiner is the author of Don't Try This at Home! The Physics of Hollywood Movies.