What principle allows a person to inch across frictionless ice to shore?

In the scenario of a person inching across frictionless ice to reach shore, the principle that applies is Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When a person pushes against the ice to move forward, they exert a force on the ice. According to Newton's third law, the ice exerts an equal and opposite force against the person's feet. This interaction allows the person to gain momentum in the direction opposite to that of the force they applied.

On frictionless ice, where there is minimal resistance, the only way for the person to move is by using their own body to create this action and reaction. This is why the person can inch toward the shore, as the forward motion is a direct consequence of the reaction force provided by the ice.

The other principles, while relevant in different contexts, do not describe the specific mechanics governing this particular motion on frictionless ice. Newton's first law relates to inertia and states that an object will remain at rest or in uniform motion unless acted upon by a net force, which doesn't apply here when the person initiates movement. Newton's second law pertains to the relationship between force, mass, and acceleration and is more focused on how forces result