Radial force generally means a force exerted in a radial direction towards the centre or away from the centre. In centrifugal pumps, radial force (also radial thrust) is the term used to designate the force acting on the pump rotor.

As a bucket of water is tied to a string and spun in a circle, the tension force acting upon the bucket provides the centripetal force required for circular motion. As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion.

Tangential force is defined as the force acting on a moving body in the direction of the tangent to the curved path of the body. If the velocity of the object is positive, the acceleration will be negative. Σ F = ma shows that an unbalanced force must be acting to cause the deceleration.

A radial force is its own type of force, like how gravity or friction are forces. Any force (or it least a component) can be considered “radial” if it has a radial component, i.e. perpendicular to the the velocity. For any circular-type motion this can be stated as ΣF=mv2r.

Circular motion is very common and very important in our everyday life. Satellites, the moon, the solar system and stars in galaxies all rotate in “circular” orbits. The term circular here is being used loosely since even repetitive closed motion is generally not a perfect circle.

As an object moves in a circle, it is constantly changing its direction. Accelerating objects are objects which are changing their velocity – either the speed (i.e., magnitude of the velocity vector) or the direction. An object undergoing uniform circular motion is moving with a constant speed.