Why does magnetic force change a charged particle’s direction without changing its speed?

The magnetic force exerted on a moving charged particle—a component of the Lorentz force—changes the particle's direction without altering its speed because the force always acts perpendicular to the particle's velocity.12

In physics, work is defined by the displacement of an object in the direction of an applied force. Because the magnetic force is always at a right angle to the direction of motion, it does no work on the particle. Since the kinetic energy of the particle remains constant when no work is performed, its speed cannot change. Instead, this perpendicular force acts as a centripetal force, continuously redirecting the particle's path—often into a circular or helical trajectory—without increasing or decreasing its velocity magnitude.132