The sentence can be completed as follows:
The motion of an object moving with uniform circular motion is always tangential to the circle, so the speed of an object moving in a circle is known as tangential speed.
The object moves by uniform circular motion due to the presence of a force (called centripetal force) pointing toward the center of the circle. Due to the presence of this force, the object experiences an acceleration (called centripetal acceleration) that makes the object turning in a circle. This centripetal acceleration changes only the direction of the velocity of the object, not its magnitude, which is called tangential speed and it is constant.
