A bowling ball sits at rest. Another ball rolls down a lane at constant speed. Which, if either, is in equilibrium? Defend your answer.

We will apply Newton's first law to define the balance on a body. A particle is considered to be in equilibrium when the result of several forces acting on it is equal to zero. In this way a body is in static equilibrium when it is at rest and no force acts on it and is considered in dynamic equilibrium when the body travels at constant speed without any force acting on it.

Therefore, according to these definitions both bodies are in a type of equilibrium: Dynamic and static.