Foot Tapping
When watching guitarists play guitar, you may notice that some guitarists tap their feet. This is because having parts of their bodies moving to the beat of the music helps guitarists play the beat that they are trying to create.
When a guitarist taps their foot, their foot has to oppose the force of gravity, like any other object that is being lifted. However, since there is a normal force on the foot that is perpendicular to the ground, the normal force on the foot changes as the person taps their foot. If their heel stays on the ground and their toes are being lifted up, then the normal force stays on their heel. However, the normal force, from the ground to their toes, is only present part of the time.