A curl of a vector field or sum must be a vector field or vector sum. At any point in the vector field, Carl explains the rotation of that point. A vector whose curl is zero is called a non-rotating or conserving vector. Vectors whose curls are not zero are called rotating or non-rotating vectors. A ball field with zero curl is called a conservative force field. Curl's divergence in a vector field is zero. The curl of a gradient in a scalar field is zero.