12.2.1—A force of constant magnitude that is always perpendicular to the direction

A force always perpendicular to instantaneous velocity does no work, so speed stays constant while the velocity direction changes.

The force direction must continuously turn with the motion; a single perpendicular impulse is not uniform circular motion by itself.

Tension toward the centre keeps a stone moving around a circle at constant speed while doing no work.

Zero work does not mean zero force or zero acceleration; direction can change with unchanged kinetic energy.