Final answer:
Vortex stretching refers to the elongation of a vortex within a fluid, often explained via the conservation of angular momentum, involving centripetal force and fluid pressure changes. In a circular motion, the centripetal force is the tension in the string that stretches it, caused by the mass's tendency to move straight and the string's redirection towards the center, as per Newton's laws.
Step-by-step explanation:
Vortex stretching refers to the elongation of a vortex line or tube within a fluid, which can occur when there is a difference in the velocity of the fluid across the vortex line. This process plays a role in the dynamics of vortices in fluid flows and is particularly significant in turbulent flows. The physical principle used to explain vortex stretching is chiefly based on the conservation of angular momentum and involves centripetal force and changes in pressure within the fluid.
In the scenario where a mass moves in a circular path on a frictionless table, the force stretching the string is the centripetal force. The physical origin of this force comes from the mass's inertia, which through Newton's first law, tends to move in a straight line at constant velocity. However, the string prevents the mass from doing this and redirects the mass towards the center of the circle, thus stretching the string. This action is also in accordance with Newton's third law, which states that for every action, there is an equal and opposite reaction. The mass acts on the string producing a tension, which is the force that stretches the string.