Fluid flow out of a nozzle

When air or any fluid is forced out of a nozzle, the fluid that is about to be forced out is under a lot of pressure. It exits at a tremendous speed, too.

Think of an infinitesimal volume of fluid that escapes the nozzle. Due to its high volocity, forces like viscosity of air, gravity, and buoyancy don't (initially) change it's trajectory significantly. Although these forces come into play a little later, the infinitesimal volume will flow in a fairly straight trajectory until then.

Whether the fluid will exit the nozzle at a variety of angles is a matter of construction of the nozzle. If the nozzle is circularly symmetric, it will leave in a cone (or a line). While a square shaped one will produce a different result (or again, a straight line).

Think of a water gun; the water leaves in a straight line. While from a deodorant can, it leaves in a cone. The conical shape being because the liquid can eject at a variety of angles from the hole. And the distribution of fluid has an axis of symmetry (the cone's axis).

Calculation of vertex angle: I'm not sure if this can be done with basic laws of physics, though it will probably need a model/approximation of sorts to find.