The last part of simulating believable objects in the game world is adding constraints to our GameObjects. Constraints allow us to take objects with Rigidbody dynamics and add constraints (limitations) on how they are affected. A good example is a hinged object like a trapdoor. Adding a force against the trapdoor would allow it to drop, but the door would just fall with gravity (either indefinitely or until it hits another collidable object).

By adding a hinge constraint, we are able to tell the physics engine that this object has a point on it that will constrain it to its position but allow it to rotate with the force of gravity pulling on it. By constraining its position and allowing its rotation only in a single axis, we have ...

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