Impulse is defined in physics as the change in momentum of an object and is calculated as the product of the net force applied and the time interval over which the force acts. Quantitatively, it is represented by the integral of force with respect to time. The magnitude of impulse is proportional to the change in the object's momentum ($\Delta p$), meaning it is the physical quantity responsible for altering the object's velocity or state of motion. Both force and time are standard physical measurements, and consequently, the unit of impulse is typically the newton-second (Ns). This concept is critical for understanding collisions, acceleration, and the mechanical interaction between bodies.