Water jet cutting works by forcing a large volume of water through a small orifice in the nozzle .The constant volume of water traveling through a reduced area causes the particles to accelerate .This accelerated stream leaving the nozzle impacts the material to be cut. The extreme pressure of the accelerated water particles contacts a small area of the work piece. In this small area the work piece develops small cracks due to stream impact. The water jet washes away the material that "erodes" from the surface of the work piece. The crack caused by the water jet impact is now exposed to the water jet the extreme pressure and impact of particles in the following stream cause the small crack to propagate until the material is cut through.