Decomposition of force Two points AB on two vertical wooden poles are equal in height. A smooth light rope is tied at two points ab. a hook is hung on the rope in the middle and a heavy object is tied below. Now, raise the right rope end from point B along the pole to point B '(the rope length is greater than the distance between ab'), and the tension of the light rope between two points ab 'will remain unchanged compared with before moving. Why remain unchanged? Why is the rope length greater than the distance between ab'?

Decomposition of force Two points AB on two vertical wooden poles are equal in height. A smooth light rope is tied at two points ab. a hook is hung on the rope in the middle and a heavy object is tied below. Now, raise the right rope end from point B along the pole to point B '(the rope length is greater than the distance between ab'), and the tension of the light rope between two points ab 'will remain unchanged compared with before moving. Why remain unchanged? Why is the rope length greater than the distance between ab'?

First of all, the forces on both sides of the pulley are equal, that is to say, the forces on both sides of the pulley are equal. Therefore, the forces on both sides of the pulley form an isosceles triangle. No matter whether point B rises or falls, as long as the distance between the two rods remains the same, you will find that the pulley always slides along the direction of the dotted line