A tightrope walker needs a balance bar to keep balance, which is based on the lever principle. The balance bar in hand is to stabilize the center of gravity of the whole human body, which can be adjusted at any time to ensure that the gravity line of the human body falls on the steel wire.
From the point of view of mechanics, if any object wants to keep balance, its gravity action line (vertical line through the center of gravity) must pass through the supporting surface (the contact surface between the object and the object supporting it). If the line of gravity does not pass through the bearing surface, the object will fall. The condition for a person to stand on the flat ground and not fall (that is, to maintain a stable balance) is that the line of gravity acting through the center of gravity of a person should be in the supporting surface formed by the outer edges of his feet.
Walking is unstable and balanced. When walking, one foot strides forward and the body leans forward. The gravity action line led down from the center of gravity goes beyond the bottom of the foot, so the person falls forward. However, before this fall action is realized, the foot in the air soon falls on the ground in front of the gravity action line led down from the center of gravity, making the action line return to the area between the two feet, so the foot falls The lost balance was restored.