A Newton-second is a unit of measurement in physics that represents the amount of momentum an object has. It is derived from the Newton, which measures force, and the second, which measures time. One Newton-second is the momentum gained by an object when a force of one Newton is applied for one second. Momentum is calculated as the product of an object's mass and its velocity. Therefore, when a force acts on an object, it changes the object's momentum over time. Understanding Newton-seconds helps in analyzing the motion of objects in various fields, including mechanics and engineering.