# It's a Goo-d Thing

While we have talked about how spring physics can be used to approximate physics of other objects within games, and how we can use them as a tethering model for in-game cameras, the physics of springs can also be used as a major component of the actual game play. One such example of using spring physics as a majorgame play mechanic is the video game called "World of Goo". The basic game play mechanic of this game is to build structures out of your main resource, Goo Balls. When goo balls are in close enough proximity to each other, they form a strut between themselves. This basic construction allows the player to build towers or bridges from the goo balls to reach the goal point of the various levels. When the player starts to build tower structures in the game, many various elements of physics have to be dealt with; spring physics and centers of gravity primarily.

### The Leaning Tower of Goo

When building a "tower of goo", the connections between goo balls start to display their spring like properties. When a tower of goo is tall enough, it starts to sway in some of the gentle breezes that occasionally pass over parts of the world. If the upper part of our structure moves far enough to one side, it is no longer over its center of gravity. If a tower starts leaning to the right, connections near the base start to compress, just as a spring would. Connections on the opposite side of the leaning start to stretch, also like a spring. If players don't adequately take measures to re-balance the tower, one of two things likely happen. The compressed connections give way and the tower falls, or the stretched springs reach their breaking point, and the tower still falls.

In the image below, we see the towers center of gravity is no longer over the lower part of the tower. When the towers center of gravity is no longer above the bulk of its lower structure, it risks falling. As it starts leaning far enough to one size, it starts to have an effect on the "goo struts" that make up its structure. On the side opposite the lean, marked by the letter A the spring starts to extend past its relaxed point, on the side the tower is leaning, marked by the letter B, the "goo strut" starts to compress.

The video below is some footage of the game play of world of goo. We can see that as the tower grows taller, winds start to effect it. The player has to keep the top in relative equilibrium to avoid overstressing the "goo struts" on the outer edges towards the bottom.