The physics tag specifies the type and properties of the dynamics engine. The type of the dynamics engine. Currently must be set to ode Rate at which to update the physics engine Maximum number of contacts allowed between two entities. This value can be over ridden by a max_contacts element in a collision element. The gravity vector Bullet specific physics properties Time step ODE specific physics properties One of the following types: world, quick The time duration which advances with each iteration of the dynamics engine. Number of iterations for each step. A higher number produces greater accuracy at a performance cost. Set the successive over-relaxation parameter. Constraint force mixing parameter. See the ODE page for more information. Error reduction parameter. See the ODE page for more information. The maximum correcting velocities allowed when resolving contacts. The depth of the surface layer around all geometry objects. Contacts are allowed to sink into the surface layer up to the given depth before coming to rest. The default value is zero. Increasing this to some small value (e.g. 0.001) can help prevent jittering problems due to contacts being repeatedly made and broken.