Well for anything curved there is more tension in the middle compared to the ends. Maybe it's the same thing.
Because of mass. But WHAT is mass?
A measure of a particle's energy as pertains to the spacetime curvature it induces
This is incorrect all the energy of a particle curves space.
Even velocity and potential energy.
Right, so those kinds of energy also induce spacetime curvature and are included in what I was saying
Wikipedia says “the property of "mass" is a manifestation of potential energy transferred to fundamental particles when they interact ("couple") with the Higgs field, which had contained that mass in the form of energy.”
Energy, not mass. Photons also curve space in this way.