Going round in circles: shrimp boat at Silloth

The Jaana B was off the promenade at Silloth. The water being pumped out of the side was pushing the boat round in circles. This is due to two of Newton's Laws of Motion. The second law says that the resultant force is equal to the rate of change of momentum. Now the water is changing momentum when pumped, going from no speed to speed v. If the rate of mass flow is dm/dt (ie m kg per second), then the rate of change of momentum is v.dm/dt. By Newton's Third Law, if the boat pushes on the water, then the water pushes back on the boat with the same size of force but in the opposite direction. Since the pump outlet is off centre, a resultant torque is created which drives the boat round in a circle.