# Why is tension constant in a massless rope? [duplicate]

This question already has an answer here:

This question does a good job explaining why tension is the same. However, I don't understand the part when he says:

"This upward movement would relax the tension in the upper part of the rope ($T_t$ decreases) and increase the tension in the lower part of the rope ($T_b$ increases). This will continue until $T_t$ equals $T_b$ and there is no net force on the rope".

Why does the movement of the rope segment, altering its location, have an affect on the Tb and Tt. Shouldn't the two tensions be constant no matter where they are in the system. Why does Tt moving up lower/relax its tension? And why does Tb moving up increase its tension.

## marked as duplicate by Qmechanic♦Feb 19 '17 at 0:10

• It should be an enough argument that $T_t-T_b=ma=0$ thus $T_t=T_b$ – user126422 Feb 18 '17 at 22:59