Besiege is a physics based game where players build medieval siege engines to destroy their foes. In the game you use things like springs, motors, wood blocks, and wheels to build almost anything you can imagine. Say you want to build a catapult to take down that castle in front of you, no problem. Before you begin launching projectiles out of the catapult, make sure it either has a counter weight or a suspension system to keep the catapult where it is. If you forgot to do this, the catapult will be carried by the momentum of the lever that is launching the projectile. The catapult will launch its self forward and destroy itself which is no good for you, But you can prevent this. By putting a counter weight you can weigh down the catapult just enough so that it stays where it is or if you want to be a little more fancy you can put a suspension system in. The springs will absorb the thrust from the projectile and distribute it throughout the catapult keeping it form flying away. While the physics of this game are not 100% accurate they are very close and can get you're brain really thinking.