Even though agents are simulated with physics, not all of the agent's physics parameters are enforced at the physics simulation level. The mass of an agent, for example, is the identical mass used within the physics simulation itself, while the MaxForce and MaxSpeed functions of an agent are only enforced by the agent. These two properties represent the maximum amount of force an agent can exert on itself and the max speed the agent can reach without any outside influences.

An intuitive example of why this separation is desirable when dealing with agent physics is gravity. When an agent accelerates to its max speed, we still want gravity to accelerate the agents downward in the case of falls. This acceleration can force agents to have a speed larger than their max speed property.

local mass = agent:GetMass();
agent:SetMass(mass);