Which specific activity does a 'funambulist' perform at a circus?

Tightrope walking, also called funambulism, is the skill of walking along a thin wire or rope. It has a long tradition in various countries and is commonly associated with the circus. Other skills similar to tightrope walking include slack rope walking and slacklining.

Funambulists maintain their balance by positioning their centre of mass directly over their base of support, i.e. shifting most of their weight over their legs, arms, or whatever part of their body they are using to hold them up. When they are on the ground with their feet side by side, the base of support is wide in the lateral direction but narrow in the sagittal (back-to-front) direction. In the case of highwire-walkers, their feet are parallel with each other, one foot positioned in front of the other while on the wire. Therefore, a tightwire walker's sway is side to side, their lateral support having been drastically reduced. In both cases, whether side by side or parallel, the ankle is the pivot point.

A wire-walker may use a pole for balance or may stretch out his arms perpendicular to his trunk in the manner of a pole. This technique provides several advantages. It distributes mass away from the pivot point, thereby increasing the moment of inertia. This reduces angular acceleration, so a greater torque is required to rotate the performer over the wire. The result is less tipping. The performer can also correct sway by rotating the pole. This will create an equal and opposite torque on the body.