sentences:  In the above example, the ground reaction force coincides with the notion of a normal force.However, in a more general case, the GRF will also have a component parallel to the ground, for example when the person is walking – a motion that requires the exchange of horizontal (frictional) forces with the ground.The use of the word reaction derives from Newton's third law, which essentially states that if a force, called "action", acts upon a body, then an equal and opposite force, called "reaction", must act upon another body.