An object in equilibrium has a net force of
. static equilibrium describes an object at
having equal and balanced forces acting upon it. dynamic equilibrium describes an object in
having equal and balanced forces acting upon it.

An object in equilibrium has a net force of zero  

Static equilibrium describes an object at  rest having equal and balanced forces acting upon it.

Dynamic equilibrium describes an object in  motion having equal and balanced forces acting upon it.

Explanation:

An object is said to be in equilibrium when a net force of zero is acting on it. When this condition occurs, the object will have zero acceleration, according to Newton's second law:

where F is the net force, m the mass of the object, a the acceleration. Since F=0, then a=0. As a result, we have two possible situations:

- If the object was at rest, then it will keep its state of rest. In this case, we talk about static equilibrium.

- If the object was moving, it will keep moving with constant velocity. In this case, we talk about dynamic equilibrium.

kepler used the data from tycho blahe (his mentor) to construct the laws of planetary motion.